Chapter 2 (textbook)

chalcogen

element in group 16

nonmetals

elements that appear dull, poor conductors of heat and electricity—shaded green

metalloids

elements that conduct heat and electricity moderately well, and possess some properties of metals and some properties of nonmetals—shaded purple

what is gemstone sapphire made of?

Aluminum Oxide. Al203.

How is a molecule's identity determined?

by the numbers and types of atoms it contains, and how they are bonded together.

metals

elements that are shiny, malleable, good conductors of heat and electricity—shaded yellow

Halogens

group 17

transition metals

groups 3-12

monoatomic ions

ions formed from a single atom

mass spectrometry- bozeman

-a way we can separate atoms, isotopes, even fragments of molecules based on their mass, very effective machine -Dalton was one of pioneers of modern chemistry. Was presenting at a conference in 1803 when he put forward his Dalton's atomic theory. Think about which of these have we changed in the past 200 hundred plus years? 1. elements are made of extremely small particles called atoms 2. atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties 3. atoms cannot be subdivided, created, or destroyed. 4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds 5. In chemical reactions, atoms are combined, separated, or rearranged Two errors: 1, are all atoms of the same element going to have the same mass? No, there are isotopes, same element diff number neutrons 2, we can subdivide atoms, so when we're looking at fusion or fission, but those really lay outside of normal chemistry We are focusing on first error, identification of isotopes. MS is a way that we can modify Dalton's atomic theory and we did that through the identification of isotopes and that was around the early part of the 1900s. Isotopes are same element but will have a different mass which is based on number of neutrons they have. What we can do from that is we can eventually calculate the average atomic mass and that's going to be on the periodic table sometimes referred to as the atomic weight. Also MS can be used to look at individual atoms, elements in a sample, and we can even break apart big macromolecules and look at the fragments that are found within that or molecules within it. If we look at a basic mass spectroscope what we are going to see is three parts: we are going to have an ionizer, a mass analyzer, and then a detector. Let's look inside the ionizer what are we going to find? The first thing we are going to find is it is a total vacuum. In other words this doesn't work unless we remove all of the gas particles found inside the mass spec, the next thing we are going to do is we are going to insert our sample in, that could be a solid, it could be a liquid, it could be a gas, but we are going to inject it into this ionizing tube, and then we are going to hit it with electrons so we're gonna move electrons through the sample, so there's a little cathode ray tube it produces all these electrons and what it's going to do is it's going to pull electrons away from the sample. As it does that it will create a number of ions and so we are going to ionize this sample inside here. It is still the sample it's just ionized- has lost its electrons. Now to mass analyzer which will have two parts in it. It will have an electric field which is - because we want to move the ions into the mass analyzer. Then we will have a magnet which is going to bend the path of the ions. As we are bending the path of the ions, it's just like driving around a corner, if you're really heavy it's harder for you to make a corner. But if you're smaller it's easier to make it. This is where we are going to figure out the difference between the mass of those ions. Then finally we have detector. Made up of 2 things- multiplier & amplifier. An electron multiplier which is essentially a plate, as electron hits it, it spawns more electrons which hit the next plate which spawns more electrons so we could really have a small amount of ions or anything hitting that plate, and we are going to get a signal. Now, that signal has to be amplified but eventually we can send that into a computer and we can look at the spectrum coming from those different masses. First you have to calibrate machine. What does that mean? You're going to start sending ions thru. So that ion didn't hit the detector, why is that, it's b/c the magnet is turned up too high, so we are going to have to lower the strength of that electromagnet, we run another ion, ok now magnet now quite strong enough, so now we run another ion, another ion, ok so we've calibrated it it seems like it is working well. Which of these cations would be heavier? Well, the ones that are heavier are the ones that can't quite make the corner so they're going to end up higher and the lighter ions lower. Let's get to some sampling. This is what it will look like when we create a spectrum, we're going to have the different weights across the bottom, and then we're going to have the intensity so wherever the intensity is high we are going to have peaks which means we have a lot of ions with that specific atomic weight. Let's try chlorine so we're going to put Cl through here. Cl really only has two stable isotopes: Chlorine-35 & Chlorine-37. What do we find? Two types of ions, two peaks. Which one will be the chlorine-37 which will be the heavier ion, well that's the higher one b/c it's not bent as much using that magnet. You can see that Chlorine-37 doesn't quite make it around the corner and which do we have more of? Well, we're going to have more of those with an atomic mass of 35.

Cathode ray tube experiment (the ochem tutor)

-experiment performed by JJ Thomsen, he used it to discover the presence of electrons inside of atoms, and also he was able to calculate the charge to mass ratio of an electron. -Let's talk about the cathode ray tube experiment. Inside this device is an evacuated chamber. The pressure is very low. Most of the gas molecules have been removed such that the pressure is as low as 0.01 pascals (Pa). At sea level, the pressure is 1 atm (equals 101, 325 Pa) so you can see the difference between the air pressure that we breathe, and the very low air pressure inside of this evacuated chamber. If pressure is too high, the electrons will collide with the gas particles, and you won't get the same effect, it won't be visible. -Now, inside the cathode ray tube we have something called a cathode, and an anode. These are two different electrodes. The cathode is a negatively charged electrode, and the anode is a positively charged electrode. When the cathode is heated by this heating element, nichrome is a good heating element, when it is heated and if there is a high voltage applied between the cathode and the anode, an electron beam is going to emanate from the cathode and it is going to accelerate towards the anode. The electrons are negatively charged, so they are attracted to a positively charged plate. So this anode accelerates this electron beam towards the right. Now, the glass of this chamber is coated with a phosphorescence material known as zinc sulfide, and so when the electrons strike the glass they exhibit this characteristic green glow. These cathode ray tubes, aka CRTs, they were very useful in making TVs in the old days, those big large TVs contained the cathode ray tube device inside of it. So when the electron beam strikes the screen, it will produce a characteristic image based on the voltage varying signal that is applied to it. -Why was this experiment called the cathode ray tube experiment and not the anode ray tube experiment? Because the electron ray appears to emanate from the cathode and not the anode and so it is called the cathode ray. -What about this experiment helped JJ Thomsen to conclude that all atoms contain electrons, negatively charged particles. How did he determine that this beam consists of negatively charged particles? Well the first thing is that this beam consists of charged particles b/c if you were to put a magnet next to it, the beam would deflect. A magnet will only deflect moving charges. It won't deflect stationary charges. So, any object that is charged and that is moving, can be deflected by a magnet. The second thing is if you apply, let me put a + charged plate on top a negatively charged plate on bottom, the beam will also be deflected. Would you say it will deflect in the upward direction or the downward direction? In this experiment, the e- ray was deflected towards the + charged plate (upward direction) so, therefore, we know that opposites attract, that means that the beam must consist of negatively charged particles. So that is how JJ Thomson came to the conclusion that this beam of particles must be negatively charged. It is due to the fact that it was deflected toward the + charged plate. E-s are attracted to + charges, opposite charges attract. Another thing that he experimented was with the use of different anode and cathode materials. It doesn't matter what metal the anode and cathode were made of. If we use zinc, aluminum, iron metal, copper, silver, all of these metals can emit a cathode ray. So the fact that these different metals can emit a cathode ray helped him to conclude that all atoms, not just certain types of atoms, all materials, all atoms, contained negatively charged particles which we now know as electrons. So now we understand how JJ Thomson was able to use the cathode ray tube experiment to determine the fact that atoms contain negatively charged particles known as electrons. But now what about calculating the charge to mass ratio of an electron? How did he use this experiment to get that number? Well, now we need to jump into the realm of physics. Let's talk about an e-. If we have a + charged plate and a - charged plate, the e- will feel a force that will attract/accelerate it towards the + charged plate, it will also feel another force that will repel it from the negatively charged plate. So, electrons can be accelerated by electric fields. They can also be accelerated by magnetic fields as well. A magnetic field can cause an e- to change direction. Not necessarily speed it up, but it can accelerate it in a way that it can cause it to change direction it can deflect it. We're going to talk about that... Let's say we have an electron that is moving towards the right, that is in the positive X direction. And we have a magnetic field that is coming out of the page. The electron will feel a force that will accelerate it in the north direction, or you could say in the + y direction if you view it from a 2 dimensional perspective. In a 3D perspective that would be the Z direction. The e- is moving towards the right, but it feels a force that is accelerating it in north direction, where will it go? In this case, it will deflect in this direction... notice you could extend this to make a circle. So by calculating the radius of curviture, and knowing the strength of the magnetic field (B), and the strength of the electric field, you could actually calculate the charge to mass ratio. New drawing- let's say this point represents the electron. It's moving towards the right so it has a velocity component in the positive x direction. The magnetic field is represented by B and it's going to be in the positive y direction from the 3d perspective. And the magnetic force acting on the electron, F sub B (FB), to indicate magnetic force, that is in the positive Z direction. The e- is going to turn/travel in the direction of the force. We can calculate the radius of curvature. Let's go over some physics equations: The magnetic force (FB) that acts on the moving charge not a stationary charge, but a moving charge, is equal to the strength of the magnetic field B, which is measured in units of tesla, times the charge of the e- (q), times the velocity of the e- (V) FB = BqV So if it's not moving the velocity will be 0 and FB/magnetic force will be 0. But as speed (V) increases, the magnetic force (FB) will increase as well proportionally. So you can increase the magnetic force acting on an e- by increasing the e- speed, or by increasing the strength of the magnetic field. Now, there's another type of force that occurs when an object moves in a circle this is known as centripetal force. The centripetal force is not a force in itself, it is caused by another force that causes the object to turn in a circle. So, if you think about how the moon orbits the earth, gravity provides the centripital force in that case. In the case of the e- turning, the magnetic force provides the centripetal force. So any force that causes an object to move in a circle, is a centripetal force and is equal to mc^2 over R. Fc = mc^2/R So b/c the magnetic force provides the centripetal force in this ex, we can set these two forces, FB and Fc, equal to eachother. BqV =. mV^2/R If we divide both sides by V, we are going to get Bq = mV/R m is the mass of the e-, V is the speed/velocity of the e-, and R is the radius of curvature. So to get the charge to mass ratio, we need to get q over m. So multiply both sides by 1/B, and also by 1/m... (1/Bm) Bq = mV/R (1/Bm) On the left B will cancel. On the right m will cancel. q/m = V/BR q is the charge of the e-, m is the mass of the e-, V is the speed, B is the strength of the magnetic field, and R is the radius. We can easily determine the strength of the magnetic field b/c we can control the amount that we apply in the experiment. We can measure radius of curvature. But measuring the speed of e- is not easy to do so we must remove from equation. The magnetic force acting on moving charged particle (FB) as we said before is equal to BqV FB = BqV The electric field, or rather the electric force, acting on any charged particle, regardless if it is moving or if it stationary, is equal to the charge of that particle, times the electric field. FE = qE We need to set this experiment in such a way that these two forces are equal and that they cancel out. If we can do that then we can set bqV = qE div both sides by q BV = E Div both sides by B we get the speed of the e- is equal to electric field div by magnetic field V = E/B If we designed the experiment in such a way that FB and FE are equal. So we could replace V with E/B. q/m = (1/BR) (E/B) Charge div by mass is equal to the electric field div by the square of the magnetic field times the radius of curvature q/m = E/(B^2)(R) Let me show you how we could set this experiment up such that the magnetic force cancels the electric force. Let's say we have 2 plates one is + charged the other is - charged. Let's say we have an e- beam that is traveling in this direction (to the right). There is gonna be an electric field that emanates from the positively charged plate and flows towards the negatively charged plate. Now, a positively charged particle like a proton, will feel an electric force (FE) that will accelerate it in the direction of the electric field. In this case it will accelerate it towards the negatively charged plate. A negatively charged particle, like an e-, will feel an electric force that will accelerate it in the other direction that is opposite to the direction of the electric field. So it will be accelerated toward the positively charged plate. So the electrons in this electron beam, they will want to deviate towards the positively charged plate. This is due to the electric force (FE) acting on them. Now if we have a magnetic force (B) that is directed into the page (BX), using the right hand rule, you could determine the direction of the magnetic force on the e-. Using your right hand, place your four fingers into the page, and you want your thumb directed in the direction of the electrons. So you want your thumb pointing towards the right, your four fingers pointing into the page, your right hand should be opening in the upward direction. The magnetic force (FB) will in the upward direction for a + charged particle, but for a - charged particle it's going to be in the downward/opposite direction using the right hand rule. Know that when magnetic field is directed into the page (B+), the electrons will feel a force that will direct them this way (down) due to the magnetic force (FB). Now if we could design the experiment in such a way that these two forces, FB and FE, are equal, they will cancel out, and so the electrons will continue to move straight to the right. So that is why we can set FB equal FE to get this equation. It all depends on if we can balance those two forces. If we could, then we can calculate that charge to mass ratio using this formula: (q/m) = E/(B^2)(R) Now once the beam of electrons passes through the electric field, what is going to happen is it is going to turn b/c the magnetic field is still active everywhere. Let's say material here. Once it escapes from electric field, and the magnetic field is the only force acting on it, it will turn and act somewhere along this spot. Then we can calculate the radius of curvature. So now we know the strength of the electric field we are applying (E), the strength of the magnetic field (B^2), and the radius of curvature, we can now calculate charge to mass ratio. So JJ Thomson discovered that the charge to mass ratio of the e-... q/m = -1.76 x 10^8 c/g Now, we actually know the charge of an e- and the mass. He didn't know at the time. qe/m = -1.602 x 10^-19 c/ 9.11 x 10^-28 g = that above number https://www.youtube.com/watch?v=i6zyPOSreCg&t=451s

Charges of Mercury

1+ (mercurous), 2+ (mercuric)

molecular formula

A molecular formula is a representation of a molecule that uses chemical symbols to indicate the types of atoms followed by subscripts to show the number of atoms of each type in the molecule. (A subscript is used only when more than one atom of a given type is present.) Molecular formulas are also used as abbreviations for the names of compounds.

What are the masses and charges of subatomic particles?

A proton has a mass of 1.0073 amu and a charge of 1+. A neutron is a slightly heavier particle with a mass 1.0087 amu and a charge of zero; as its name suggests, it is neutral. The electron has a charge of 1− and is a much lighter particle with a mass of about 0.00055 amu (it would take about 1800 electrons to equal the mass of one proton). An observant student might notice that the sum of an atom's subatomic particles does not equal the atom's actual mass: The total mass of six protons, six neutrons, and six electrons is 12.0993 amu, slightly larger than 12.00 amu. This "missing" mass is known as the mass defect, and you will learn about it in the chapter on nuclear chemistry.)

Parts per billion by mass (ppb)

mass of solute/mass of solution x 10^9

hydrogen is

reactive nonmetal

mass number

The total number of protons and neutrons in an atom is called its mass number (A). The number of neutrons is therefore the difference between the mass number and the atomic number: A - Z = number of neutrons.

alkali metals

Group 1, 1 electron in outer level, very reactive, soft, silver, shiny, low density; Lithium, Sodium, Potassium, Rubidium, Cesium, Francium the elements in group 1 (the first column) form compounds that consist of one atom of the element and one atom of hydrogen. These elements (except hydrogen) are known as alkali metals, and they all have similar chemical properties.

Chalcogens

Group 16 (6A) Oxygen family/group

Halogens

Group 17

Hydrogen

Hydrogen is a unique, nonmetallic element with properties similar to both group 1 and group 17 elements. For that reason, hydrogen may be shown at the top of both groups, or by itself.

Determining Empirical Formula

If we know a compound's formula, we can easily determine the empirical formula. (This is somewhat of an academic exercise; the reverse chronology is generally followed in actual practice.) For example, the molecular formula for acetic acid, the component that gives vinegar its sharp taste, is C2H4O2. This formula indicates that a molecule of acetic acid (Figure 2.21) contains two carbon atoms, four hydrogen atoms, and two oxygen atoms. The ratio of atoms is 2:4:2. Dividing by the lowest common denominator (2) gives the simplest, whole-number ratio of atoms, 1:2:1, so the empirical formula is CH2O. Note that a molecular formula is always a whole-number multiple of an empirical formula.

types of isomers

Many types of isomers exist (Figure 2.24). Acetic acid and methyl formate are structural isomers, compounds in which the molecules differ in how the atoms are connected to each other. There are also various types of spatial isomers, in which the relative orientations of the atoms in space can be different. For example, the compound carvone (found in caraway seeds, spearmint, and mandarin orange peels) consists of two isomers that are mirror images of each other. S-(+)-carvone smells like caraway, and R-(−)-carvone smells like spearmint.

Pnictogens

Nitrogen Family Group 15/5A

covalent bonds

When electrons are "shared" and molecules form, covalent bonds result. Covalent bonds are the attractive forces between the positively charged nuclei of the bonded atoms and one or more pairs of electrons that are located between the atoms. Compounds are classified as ionic or molecular (covalent) on the basis of the bonds present in them.

Through Thomson and Millikan, what do we now know that goes against what Dalton proposed?

Scientists had now established that the atom was not indivisible as Dalton had believed, and due to the work of Thomson, Millikan, and others, the charge and mass of the negative, subatomic particles- the electrons- were known. However, the positively charged part of an atom was not yet well understood. In 1904, Thomson proposed the "plum pudding" model of atoms, which described a positively charged mass with an equal amount of negative charge in the form of electrons embedded in it, since all atoms are electrically neutral. A competing model had been proposed in 1903 by Hantaro Nagaoka, who postulated a Saturn-like atom, consisting of a positively charged sphere surrounded by a halo of electrons.

alkaline earth metals

The elements in group 2 (the second column) form compounds consisting of one atom of the element and two atoms of hydrogen: These are called alkaline earth metals, with similar properties among members of that group.

noble gases

aka inert gases group 18

main group elements

aka representative elements columns 1, 2, and 13-18

oxyanions

polyatomic ions that contain one or more oxygen atoms.

periodic law

the properties of the elements are periodic functions of their atomic numbers

inner transition metals

two rows at the bottom of the table. The top-row elements are called lanthanides and the bottom-row elements are actinides.

Dalton's atomic theory postulates:

-Published in 1807, English school teacher John Dalton helped revolutionize chemistry with his hypothesis that the behavior of matter could be explained using an atomic theory... 1. Matter is composed of exceedingly small particles called atoms. An atom is the smallest unit of an element that can participate in a chemical change. 2. An element consists of only one type of atom, which has a mass that is characteristic of the element and is the same for all atoms of that element. A macroscopic sample of an element contains an incredibly large sample of atoms, all of which have identical chemical properties. 3. Atoms of one element differ in properties from atoms of all other elements 4. A compound consists of two or more elements combined in a small, whole-number ratio. In a given compound, the numbers of atoms of each of its elements is always present in the same ratio. 5. Atoms are neither created nor destroyed during a chemical change, but are instead rearranged to yield substances that are different from those present before the change. Dalton's atomic theory provides a microscopic explanation of the many macroscopic properties of matter that you've learned about. For example, if an element such as copper consists of only one kind of atom, then it cannot be broken down into simpler substances, that is, into substances composed of fewer types of atoms. And if atoms are neither created nor destroyed during a chemical change, then the total mass of matter present when matter changes from one type to another will remain constant (the law of conservation of matter).

how to write a charge

4+ or 4- (sign comes after number)

rules for naming binary covalent compounds

A binary covalent compound is composed of two different nonmetal elements. For example, a molecule of chlorine trifluoride, ClF3 contains 1 atom of chlorine and 3 atoms of fluorine. Rule 1. The element with the lower group number is written first in the name; the element with the higher group number is written second in the name. Exception: when the compound contains oxygen and a halogen, the name of the halogen is the first word in the name. Rule 2. If both elements are in the same group, the element with the higher period number is written first in the name. Rule 3. The second element in the name is named as if it were an anion, i.e., by adding the suffix -ide to the name of the element. Rule 4. Greek prefixes (see the Table provided at the bottom of this page) are used to indicate the number of atoms of each nonmetal element in the chemical formula for the compound. Exception: if the compound contains one atom of the element that is written first in the name, the prefix "mono-" is not used. Note: when the addition of the Greek prefix places two vowels adjacent to one another, the "a" (or the "o") at the end of the Greek prefix is usually dropped; e.g., "nonaoxide" would be written as "nonoxide", and "monooxide" would be written as "monoxide". The "i" at the end of the prefixes "di-" and "tri-" are never dropped.

chemical symbol

A chemical symbol is an abbreviation that we use to indicate an element or an atom of an element. For example, the symbol for mercury is Hg (Figure 2.13). We use the same symbol to indicate one atom of mercury (microscopic domain) or to label a container of many atoms of the element mercury (macroscopic domain).

ionic compounds

A compound that contains ions and is held together by ionic bonds is called an ionic compound. The periodic table can help us recognize many of the compounds that are ionic: When a metal is combined with one or more nonmetals, the compound is usually ionic. This guideline works well for predicting ionic compound formation for most of the compounds typically encountered in an introductory chemistry course. However, it is not always true (for example, aluminum chloride, AlCl3, is not ionic).

periodic table

A modern periodic table arranges the elements in increasing order of their atomic numbers and groups atoms with similar properties in the same vertical column. Each box represents an element and contains its atomic number, symbol, average atomic mass, and (sometimes) name.

elements that exist as molecules of one element

Although many elements consist of discrete, individual atoms, some exist as molecules made up of two or more atoms of the element chemically bonded together. For example, most samples of the elements hydrogen, oxygen, and nitrogen are composed of molecules that contain two atoms each (called diatomic molecules) and thus have the molecular formulas H2, O2, and N2, respectively. Other elements commonly found as diatomic molecules are fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2). The most common form of the element sulfur is composed of molecules that consist of eight atoms of sulfur; its molecular formula is S8 (Figure 2.17). It is important to note that a subscript following a symbol and a number in front of a symbol do not represent the same thing; for example, H2 and 2H represent distinctly different species. H2 is a molecular formula; it represents a diatomic molecule of hydrogen, consisting of two atoms of the element that are chemically bonded together. The expression 2H, on the other hand, indicates two separate hydrogen atoms that are not combined as a unit. The expression 2H2 represents two molecules of diatomic hydrogen (Figure 2.18).

alkali vs alkaline earth metals

As early chemists worked to purify ores and discovered more elements, they realized that various elements could be grouped together by their similar chemical behaviors. One such grouping includes lithium (Li), sodium (Na), and potassium (K): These elements all are shiny, conduct heat and electricity well, and have similar chemical properties. A second grouping includes calcium (Ca), strontium (Sr), and barium (Ba), which also are shiny, good conductors of heat and electricity, and have chemical properties in common. However, the specific properties of these two groupings are notably different from each other. For example: Li, Na, and K are much more reactive than are Ca, Sr, and Ba; Li, Na, and K form compounds with oxygen in a ratio of two of their atoms to one oxygen atom, whereas Ca, Sr, and Ba form compounds with one of their atoms to one oxygen atom.

anion & cation

As will be discussed in more detail later in this chapter, atoms (and molecules) typically acquire charge by gaining or losing electrons. An atom that gains one or more electrons will exhibit a negative charge and is called an anion. Positively charged atoms called cations are formed when an atom loses one or more electrons. For example, a neutral sodium atom (Z = 11) has 11 electrons. If this atom loses one electron, it will become a cation with a 1+ charge (11 − 10 = 1+). A neutral oxygen atom (Z = 8) has eight electrons, and if it gains two electrons it will become an anion with a 2− charge (8 − 10 = 2−).

ion

Atoms are electrically neutral if they contain the same number of positively charged protons and negatively charged electrons. When the numbers of these subatomic particles are not equal, the atom is electrically charged and is called an ion. The charge of an atom is defined as follows: Atomic charge = number of protons − number of electrons

You can use the periodic table to predict whether an atom will form an anion or a cation, and you can often predict the charge of the resulting ion

Atoms of many main-group metals lose enough electrons to leave them with the same number of electrons as an atom of the preceding noble gas. To illustrate, an atom of an alkali metal (group 1) loses one electron and forms a cation with a 1+ charge; an alkaline earth metal (group 2) loses two electrons and forms a cation with a 2+ charge, and so on. For example, a neutral calcium atom, with 20 protons and 20 electrons, readily loses two electrons. This results in a cation with 20 protons, 18 electrons, and a 2+ charge. It has the same number of electrons as atoms of the preceding noble gas, argon, and is symbolized Ca2+. The name of a metal ion is the same as the name of the metal atom from which it forms, so Ca2+ is called a calcium ion. When atoms of nonmetal elements form ions, they generally gain enough electrons to give them the same number of electrons as an atom of the next noble gas in the periodic table. Atoms of group 17 gain one electron and form anions with a 1− charge; atoms of group 16 gain two electrons and form ions with a 2− charge, and so on. For example, the neutral bromine atom, with 35 protons and 35 electrons, can gain one electron to provide it with 36 electrons. This results in an anion with 35 protons, 36 electrons, and a 1− charge. It has the same number of electrons as atoms of the next noble gas, krypton, and is symbolized Br−. (A discussion of the theory supporting the favored status of noble gas electron numbers reflected in these predictive rules for ion formation is provided in a later chapter of this text.) Note the usefulness of the periodic table in predicting likely ion formation and charge (Figure 2.29). Moving from the far left to the right on the periodic table, main-group elements tend to form cations with a charge equal to the group number. That is, group 1 elements form 1+ ions; group 2 elements form 2+ ions, and so on. Moving from the far right to the left on the periodic table, elements often form anions with a negative charge equal to the number of groups moved left from the noble gases. For example, group 17 elements (one group left of the noble gases) form 1− ions; group 16 elements (two groups left) form 2− ions, and so on. This trend can be used as a guide in many cases, but its predictive value decreases when moving toward the center of the periodic table. In fact, transition metals and some other metals often exhibit variable charges that are not predictable by their location in the table. For example, copper can form ions with a 1+ or 2+ charge, and iron can form ions with a 2+ or 3+ charge.

atomic mass unit (amu) & fundamental unit of charge (e)

Atoms—and the protons, neutrons, and electrons that compose them—are extremely small. For example, a carbon atom weighs less than 2 × 10−23 g, and an electron has a charge of less than 2 × 10−19 C (coulomb). When describing the properties of tiny objects such as atoms, we use appropriately small units of measure, such as the atomic mass unit (amu) and the fundamental unit of charge (e). The amu was originally defined based on hydrogen, the lightest element, then later in terms of oxygen. Since 1961, it has been defined with regard to the most abundant isotope of carbon, atoms of which are assigned masses of exactly 12 amu. (This isotope is known as "carbon-12" as will be discussed later in this module.) Thus, one amu is exactly 1 of the mass of one carbon-12 −24 12 atom: 1 amu = 1.6605 × 10 g. (The Dalton (Da) and the unified atomic mass unit (u) are alternative units that are equivalent to the amu.) The fundamental unit of charge (also called the elementary charge) equals the magnitude of the charge of an electron (e) with e = 1.602 × 10−19 C.

How do we symbolize ionic compounds?

Because an ionic compound is not made up of single, discrete molecules, it may not be properly symbolized using a molecular formula. Instead, ionic compounds must be symbolized by a formula indicating the relative numbers of its constituent ions. For compounds containing only monatomic ions (such as NaCl) and for many compounds containing polyatomic ions (such as CaSO4), these formulas are just the empirical formulas introduced earlier in this chapter. However, the formulas for some ionic compounds containing polyatomic ions are not empirical formulas. For example, the ionic compound sodium oxalate is comprised of Na+ and C2 O4 2− ions combined in a 2:1 ratio, and its formula is written as Na2C2O4. The subscripts in this formula are not the smallest-possible whole numbers, as each can be divided by 2 to yield the empirical formula, NaCO2. This is not the accepted formula for sodium oxalate, however, as it does not accurately represent the compound's polyatomic anion, C2 O4 2−.

atomic mass

Because each proton and each neutron contribute approximately one amu to the mass of an atom, and each electron contributes far less, the atomic mass of a single atom is approximately equal to its mass number (a whole number). However, the average masses of atoms of most elements are not whole numbers because most elements exist naturally as mixtures of two or more isotopes. The mass of an element shown in a periodic table or listed in a table of atomic masses is a weighted, average mass of all the isotopes present in a naturally occurring sample of that element. This is equal to the sum of each individual isotope's mass multiplied by its fractional abundance. For example, the element boron is composed of two isotopes: About 19.9% of all boron atoms are 10B with a mass of 10.0129 amu, and the remaining 80.1% are 11B with a mass of 11.0093 amu. The average atomic mass for boron is calculated to be: boron average mass = (0.199 × 10.0129 amu) + (0.801 × 11.0093 amu) = 1.99 amu + 8.82 amu = 10.81 amu It is important to understand that no single boron atom weighs exactly 10.8 amu; 10.8 amu is the average mass of all boron atoms, and individual boron atoms weigh either approximately 10 amu or 11 amu.

empirical formula

Compounds are formed when two or more elements chemically combine, resulting in the formation of bonds. For example, hydrogen and oxygen can react to form water, and sodium and chlorine can react to form table salt. We sometimes describe the composition of these compounds with an empirical formula, which indicates the types of atoms present and the simplest whole-number ratio of the number of atoms (or ions) in the compound. For example, titanium dioxide (used as pigment in white paint and in the thick, white, blocking type of sunscreen) has an empirical formula of TiO2. This identifies the elements titanium (Ti) and oxygen (O) as the constituents of titanium dioxide, and indicates the presence of twice as many atoms of the element oxygen as atoms of the element titanium (Figure 2.19). As discussed previously, we can describe a compound with a molecular formula, in which the subscripts indicate the actual numbers of atoms of each element in a molecule of the compound. In many cases, the molecular formula of a substance is derived from experimental determination of both its empirical formula and its molecular mass (the sum of atomic masses for all atoms composing the molecule). For example, it can be determined experimentally that benzene contains two elements, carbon (C) and hydrogen (H), and that for every carbon atom in benzene, there is one hydrogen atom. Thus, the empirical formula is CH. An experimental determination of the molecular mass reveals that a molecule of benzene contains six carbon atoms and six hydrogen atoms, so the molecular formula for benzene is C6H6 (Figure 2.20).

compounds containing polyatomic ions

Compounds containing polyatomic ions are named similarly to those containing only monatomic ions, i.e. by naming first the cation and then the anion. Examples are shown in Table 2.7.

Law of Multiple Proportions

Dalton also used data from Proust as well as results from his own experiments to formulate another law: law of multiple proportions when two elements form a series of compounds, the ratio of the masses of the 2nd element that combine with 1 gram of the first element can always be reduced to small whole numbers. What does that mean? Give you example. First we need to use two elements that combine to give us multiple compounds. let's use CO and C02. Both of these compounds contain the same 2 elements: carbon and oxygen. But the way that they are combined is different. These are completely different compounds. The atomic mass of C is 12, and the atomic mass of O is 16. CO: 12 g C combined with 16 g O. The first element is carbon, the second element is oxygen. We want the first element to have a mass of 1. So I divide both these numbers by 12. 12 g C = 16 g O div both by 12 1 g C = 1.33 g O So 1 g of C combines with 1.33 g O in CO. Now to C02. 12 g C = 32 g O. div both by 12. 1 g C = 2.67 g O. Let's focus on the statement. The ratio of the masses of the second element can always be reduced to small whole numbers. O is second element. This is how much O is present if we have 1 g of the first element. What is the ratio between the two bolded numbers? Well, if you take 2.67. and divide it by 1.33, this will be about 2. The reason for that is there are twice as many oxygen atoms in C02 compared to our first compound CO. That is main idea behind the law of multiple proportions, whenever you have two elements that can form a series of compounds, in the case of CO and CO2, the ratio of the masses of the second element, that combine with 1 g of the first element, can always be reduced to small, whole numbers.

Who invented the periodic table?

Dmitri Mendeleev in 1869 Dimitri Mendeleev in Russia (1869) and Lothar Meyer in Germany (1870) independently recognized that there was a periodic relationship among the properties of the elements known at that time. Both published tables with the elements arranged according to increasing atomic mass. But Mendeleev went one step further than Meyer: He used his table to predict the existence of elements that would have the properties similar to aluminum and silicon, but were yet unknown. The discoveries of gallium (1875) and germanium (1886) provided great support for Mendeleev's work. Although Mendeleev and Meyer had a long dispute over priority, Mendeleev's contributions to the development of the periodic table are now more widely recognized (Figure 2.25).

Isotopes

During early 1900s, scientists identified several substances that appeared to be new elements, isolating them from radioactive ores. For example, a "new element" produced by the radioactive decay of thorium was initially given the name mesothorium. However, a more detailed analysis showed that mesothorium was chemically identical to radium (another decay product), despite having a different atomic mass. This result, along with similar findings for other elements, led the English chemist Frederick Soddy to realize that an element could have types of atoms with different masses that were chemically indistinguishable. These different types are called isotopes—atoms of the same element that differ in mass. Soddy was awarded the Nobel Prize in Chemistry in 1921 for this discovery. One puzzle remained: The nucleus was known to contain almost all of the mass of an atom, with the number of protons only providing half, or less, of that mass. Different proposals were made to explain what constituted the remaining mass, including the existence of neutral particles in the nucleus. As you might expect, detecting uncharged particles is very challenging, and it was not until 1932 that James Chadwick found evidence of neutrons, uncharged, subatomic particles with a mass approximately the same as that of protons. The existence of the neutron also explained isotopes: They differ in mass because they have different numbers of neutrons, but they are chemically identical b/c they have the same number of protons.

Cr(VI) groundwater contamination

Erin Brokovich and Chromium Contamination In the early 1990s, legal file clerk Erin Brockovich (Figure 2.32) discovered a high rate of serious illnesses in the small town of Hinckley, California. Her investigation eventually linked the illnesses to groundwater contaminated by Cr(VI) used by Pacific Gas & Electric (PG&E) to fight corrosion in a nearby natural gas pipeline. As dramatized in the film Erin Brokovich (for which Julia Roberts won an Oscar), Erin and lawyer Edward Masry sued PG&E for contaminating the water near Hinckley in 1993. The settlement they won in 1996—$333 million—was the largest amount ever awarded for a direct-action lawsuit in the US at that time. Chromium compounds are widely used in industry, such as for chrome plating, in dye-making, as preservatives, and to prevent corrosion in cooling tower water, as occurred near Hinckley. In the environment, chromium exists primarily in either the Cr(III) or Cr(VI) forms. Cr(III), an ingredient of many vitamin and nutritional supplements, forms compounds that are not very soluble in water, and it has low toxicity. But Cr(VI) is much more toxic and forms compounds that are reasonably soluble in water. Exposure to small amounts of Cr(VI) can lead to damage of the respiratory, gastrointestinal, and immune systems, as well as the kidneys, liver, blood, and skin. Despite cleanup efforts, Cr(VI) groundwater contamination remains a problem in Hinckley and other locations across the globe. A 2010 study by the Environmental Working Group found that of 35 US cities tested, 31 had higher levels of Cr(VI) in their tap water than the public health goal of 0.02 parts per billion set by the California Environmental Protection Agency.

Halogens

Group 17 (7A) 7 valence electrons Fluorine (F), chlorine (Cl), bromine (Br), and iodine (I) also exhibit similar properties to each other, but these properties are drastically different from those of any of the elements above.

Summarize the findings of Robert A. Millikan

In 1909, more info about the e- was uncovered by American physicist Robert A. Millikan via his "oil drop" experiments. Millikan created microscopic oil droplets, which could be electrically charged by friction as they formed or by using X-rays. These droplets initially fell due to gravity, but their downward progress could be slowed or even reversed by an electric field lower in the apparatus. By adjusting the electric field strength and making careful measurements and appropriate calculations, Millikan was able to determine the charge on the individual drops. Looking at the charge data Millikan gathered, you may have recognized that the charge of an oil droplet is always a multiple of a specific charge, 1.6 x 10^-19 C. Millikan concluded that this value must therefore be a fundamental charge- the charge of a single electron- with his measured charges due to an excess of one electron (1 times 1.6 x 10^-19), two electrons (2 times 1.6 x 10^-19) and three electrons (3 times 1.6 x 10^-19) and so on on a given oil droplet. Since the charge of an e- was now known due to Millikan's research, and the charge-to-mass ratio was already known due to Thomson's research (1.759 x 10^11 C/kg), it only required a simple calculation to determine the mass of the e- as well. Mass of electron = 1.602 x 10^-19 x (1 kg/1.759 x 10^11 C) = 9.107 x 10^-31 kg

What subatomic particle is essential for bonding?

In ordinary chemical reactions, the nucleus of each atom (and thus the identity of the element) remains unchanged. Electrons, however, can be added to atoms by transfer from other atoms, lost by transfer to other atoms, or shared with other atoms. The transfer and sharing of electrons among atoms govern the chemistry of the elements. During the formation of some compounds, atoms gain or lose electrons, and form electrically charged particles called ions (Figure 2.28).

why are some atomic masses given in square brackets?

In studying the periodic table, you might have noticed something about the atomic masses of some of the elements. Element 43 (technetium), element 61 (promethium), and most of the elements with atomic number 84 (polonium) and higher have their atomic mass given in square brackets. This is done for elements that consist entirely of unstable, radioactive isotopes (you will learn more about radioactivity in the nuclear chemistry chapter). An average atomic weight cannot be determined for these elements because their radioisotopes may vary significantly in relative abundance, depending on the source, or may not even exist in nature. The number in square brackets is the atomic mass number (an approximate atomic mass) of the most stable isotope of that element.

The earliest recorded discussion of the basic structure of matter came from who and when?

In the fifth century BC, Leucippus and Democritus argued that all matter was composed of small, finite particles that they called atomos, a term derived from the Greek word "indivisible." They thought of atoms as moving particles that differed in shape and size and which could join together. Later, Aristotle and others came to the conclusion that matter consisted of various combos of the four "elements"- fire, earth, air, and water- and could be infinitely divided. These philosophers thought about atoms and "elements" as philosophical concepts but never considered performing experiments to test their ideas.

naturally occurring isotopes with atomic numbers 1 through 10

Information about the naturally occurring isotopes of elements with atomic numbers 1 through 10 is given in Table 2.4. Note that in addition to standard names and symbols, the isotopes of hydrogen are often referred to using common names and accompanying symbols. Hydrogen-2, symbolized 2H, is also called deuterium and sometimes symbolized D. Hydrogen-3, symbolized 3H, is also called tritium and sometimes symbolized T. *write this out

ionic hydrates

Ionic compounds that contain water molecules as integral components of their crystals are called hydrates. The name for an ionic hydrate is derived by adding a term to the name for the anhydrous (meaning "not hydrated") compound that indicates the number of water molecules associated with each formula unit of the compound. The added word begins with a Greek prefix denoting the number of water molecules (see Table 2.10) and ends with "hydrate." For example, the anhydrous compound copper(II) sulfate also exists as a hydrate containing five water molecules and named copper(II) sulfate pentahydrate. Washing soda is the common name for a hydrate of sodium carbonate containing 10 water molecules; the systematic name is sodium carbonate decahydrate. Formulas for ionic hydrates are written by appending a vertically centered dot, a coefficient representing the number of water molecules, and the formula for water. The two examples mentioned in the previous paragraph are represented by the formulas

isomers

It is important to be aware that it may be possible for the same atoms to be arranged in different ways: Compounds with the same molecular formula may have different atom-to-atom bonding and therefore different structures. For example, could there be another compound with the same formula as acetic acid, C2H4O2? And if so, what would be the structure of its molecules? If you predict that another compound with the formula C2H4O2 could exist, then you demonstrated good chemical insight and are correct. Two C atoms, four H atoms, and two O atoms can also be arranged to form a methyl formate, which is used in manufacturing, as an insecticide, and for quick-drying finishes. Methyl formate molecules have one of the oxygen atoms between the two carbon atoms, differing from the arrangement in acetic acid molecules. Acetic acid and methyl formate are examples of isomers—compounds with the same chemical formula but different molecular structures (Figure 2.23). Note that this small difference in the arrangement of the atoms has a major effect on their respective chemical properties. You would certainly not want to use a solution of methyl formate as a substitute for a solution of acetic acid (vinegar) when you make salad dressing.

oxyacids

Many compounds containing three or more elements (such as organic compounds or coordination compounds) are subject to specialized nomenclature rules that you will learn later. However, we will briefly discuss the important compounds known as oxyacids, compounds that contain hydrogen, oxygen, and at least one other element, and are bonded in such a way as to impart acidic properties to the compound (you will learn the details of this in a later chapter). Typical oxyacids consist of hydrogen combined with a polyatomic, oxygen-containing ion. To name oxyacids: 1. Omit "hydrogen" 2. Start with the root name of the anion 3. Replace -ate with -ic, or -ite with -ous 4. Add "acid" For example, consider H2CO3 (which you might be tempted to call "hydrogen carbonate"). To name this correctly, "hydrogen" is omitted; the -ate of carbonate is replace with -ic; and acid is added—so its name is carbonic acid. Other examples are given in Table 2.13. There are some exceptions to the general naming method (e.g., H2SO4 is called sulfuric acid, not sulfic acid, and H2SO3 is sulfurous, not sulfous, acid).

Molecular compounds

Many compounds do not contain ions but instead consist solely of discrete, neutral molecules. These molecular compounds (covalent compounds) result when atoms share, rather than transfer (gain or lose), electrons. Covalent bonding is an important and extensive concept in chemistry, and it will be treated in considerable detail in a later chapter of this text.

polyatomic ions in ionic compounds

Many ionic compounds contain polyatomic ions (Table 2.5) as the cation, the anion, or both. As with simple ionic compounds, these compounds must also be electrically neutral, so their formulas can be predicted by treating the polyatomic ions as discrete units. We use parentheses in a formula to indicate a group of atoms that behave as a unit. For example, the formula for calcium phosphate, one of the minerals in our bones, is Ca3(PO4)2. This formula indicates that there are three calcium ions (Ca2+) for every two phosphate (PO4 3−) groups. The PO4 3− groups are discrete units, each consisting of one phosphorus atom and four oxygen atoms, and having an overall charge of 3−. The compound is electrically neutral, and its formula shows a total count of three Ca, two P, and eight O atoms.

compounds containing a metal ion with a variable charge

Most of the transition metals and some main group metals can form two or more cations with different charges. Compounds of these metals with nonmetals are named with the same method as compounds in the first category, except the charge of the metal ion is specified by a Roman numeral in parentheses after the name of the metal. The charge of the metal ion is determined from the formula of the compound and the charge of the anion. For example, consider binary ionic compounds of iron and chlorine. Iron typically exhibits a charge of either 2+ or 3+ (see Figure 2.29), and the two corresponding compound formulas are FeCl2 and FeCl3. The simplest name, "iron chloride," will, in this case, be ambiguous, as it does not distinguish between these two compounds. In cases like this, the charge of the metal ion is included as a Roman numeral in parentheses immediately following the metal name. These two compounds are then unambiguously named iron(II) chloride and iron(III) chloride, respectively. Other examples are provided in Table 2.9. Out-of-date nomenclature used the suffixes -ic and -ous to designate metals with higher and lower charges, respectively: Iron(III) chloride, FeCl3, was previously called ferric chloride, and iron(II) chloride, FeCl2, was known as ferrous chloride. Though this naming convention has been largely abandoned by the scientific community, it remains in use by some segments of industry. For example, you may see the words stannous fluoride on a tube of toothpaste. This represents the formula SnF2, which is more properly named tin(II) fluoride. The other fluoride of tin is SnF4, which was previously called stannic fluoride but is now named tin(IV) fluoride.

nomenclature

Nomenclature, a collection of rules for naming things, is important in science and in many other situations. This module describes an approach that is used to name simple ionic and molecular compounds, such as NaCl, CaCO3, and N2O4. The simplest of these are binary compounds, those containing only two elements, but we will also consider how to name ionic compounds containing polyatomic ions, and one specific, very important class of compounds known as acids (subsequent chapters in this text will focus on these compounds in great detail). We will limit our attention here to inorganic compounds, compounds that are composed principally of elements other than carbon, and will follow the nomenclature guidelines proposed by IUPAC. The rules for organic compounds, in which carbon is the principle element, will be treated in a later chapter on organic chemistry. To name an inorganic compound, we need to consider the answers to several questions. First, is the compound ionic or molecular? If the compound is ionic, does the metal form ions of only one type (fixed charge) or more than one type (variable charge)? Are the ions monatomic or polyatomic? If the compound is molecular, does it contain hydrogen? If so, does it also contain oxygen? From the answers we derive, we place the compound in an appropriate category and then name it accordingly.

system for naming some polyatomic ions

Note that there is a system for naming some polyatomic ions; -ate and -ite are suffixes designating polyatomic ions containing more or fewer oxygen atoms. Per- (short for "hyper") and hypo- (meaning "under") are prefixes meaning more oxygen atoms than -ate and fewer oxygen atoms than -ite, respectively. For example, perchlorate is ClO4 − , chlorate is ClO3− , chlorite is ClO2− and hypochlorite is ClO−. Unfortunately, the number of oxygen atoms corresponding to a given suffix or prefix is not consistent; for example, nitrate is NO3 − while sulfate is SO4 2−. This will be covered in more detail in the next module on nomenclature.

binary acids

Some compounds containing hydrogen are members of an important class of substances known as acids. The chemistry of these compounds is explored in more detail in later chapters of this text, but for now, it will suffice to note that many acids release hydrogen ions, H+, when dissolved in water. To denote this distinct chemical property, a mixture of water with an acid is given a name derived from the compound's name. If the compound is a binary acid (comprised of hydrogen and one other nonmetallic element): 1. The word "hydrogen" is changed to the prefix hydro- 2. The other nonmetallic element name is modified by adding the suffix -ic 3. The word "acid" is added as a second word For example, when the gas HCl (hydrogen chloride) is dissolved in water, the solution is called hydrochloric acid. Several other examples of this nomenclature are shown in Table 2.12.

molecular (covalent) compounds

The bonding characteristics of inorganic molecular compounds are different from ionic compounds, and they are named using a different system as well. The charges of cations and anions dictate their ratios in ionic compounds, so specifying the names of the ions provides sufficient information to determine chemical formulas. However, because covalent bonding allows for significant variation in the combination ratios of the atoms in a molecule, the names for molecular compounds must explicitly identify these ratios. When two nonmetallic elements form a molecular compound, several combination ratios are often possible. For example, carbon and oxygen can form the compounds CO and CO2. Since these are different substances with different properties, they cannot both have the same name (they cannot both be called carbon oxide). To deal with this situation, we use a naming method that is somewhat similar to that used for ionic compounds, but with added prefixes to specify the numbers of atoms of each element. The name of the more metallic element (the one farther to the left and/or bottom of the periodic table) is first, followed by the name of the more nonmetallic element (the one farther to the right and/or top) with its ending changed to the suffix -ide. The numbers of atoms of each element are designated by the Greek prefixes shown in Table 2.10. When only one atom of the first element is present, the prefix mono- is usually deleted from that part. Thus, CO is named carbon monoxide, and CO2 is called carbon dioxide. When two vowels are adjacent, the a in the Greek prefix is usually dropped. Some other examples are shown in Table 2.11. There are a few common names that you will encounter as you continue your study of chemistry. For example, although NO is often called nitric oxide, its proper name is nitrogen monoxide. Similarly, N2O is known as nitrous oxide even though our rules would specify the name dinitrogen monoxide. (And H2O is usually called water, not dihydrogen monoxide.) You should commit to memory the common names of compounds as you encounter them.

modern atomic theory tells us what about the inner structure of atoms?

The development of modern atomic theory revealed much about the inner structure of atoms. It was learned that an atom contains a very small nucleus composed of positively charged protons and uncharged neutrons, surrounded by a much larger volume of space containing negatively charged electrons. The nucleus contains the majority of an atom's mass because protons and neutrons are much heavier than electrons, whereas electrons occupy almost all of an atom's volume. The diameter of an atom is on the order of 10−10 m, whereas the diameter of the nucleus is roughly 10−15 m—about 100,000 times smaller. For a perspective about their relative sizes, consider this: If the nucleus were the size of a blueberry, the atom would be about the size of a football stadium

periods & groups

The elements are arranged in seven horizontal rows, called periods or series, and 18 vertical columns, called groups. Groups are labeled at the top of each column. In the United States, the labels traditionally were numerals with capital letters. However, IUPAC recommends that the numbers 1 through 18 be used, and these labels are more common. For the table to fit on a single page, parts of two of the rows, a total of 14 columns, are usually written below the main body of the table

compounds containing only monoatomic ions

The name of a binary compound containing monatomic ions consists of the name of the cation (the name of the metal) followed by the name of the anion (the name of the nonmetallic element with its ending replaced by the suffix -ide). Some examples are given in Table 2.6.

Summarize the findings of Ernest Rutherford

The next major development in understanding the atom came from Ernest Rutherford, a physicist from New Zealand who largely spent his scientific career in Canada and England. He performed a series of experiments using a beam of high-speed, positively charged alpha particles that were produced by the radioactive decay of radium; alpha particles consisted of two protons and two neutrons. Rutherford and his colleagues Han Geiger and Ernest Marsden aimed a beam of alpha particles, the source which was embedded in a lead block to absorb most of the radiation, at a very thin piece of gold foil and examined the resultant scattering of the alpha particles using a luminescent screen that glowed briefly where hit by an alpha particle. What did they discover? Most particles passed through the foil without being deflected at all. However, some were diverted slightly, and a very small number were deflected straight back toward the source. Here is what Rutherford deduced: Because most of the fast-moving α particles passed through the gold atoms undeflected, they must have traveled through essentially empty space inside the atom. Alpha particles are positively charged, so deflections arose when they encountered another positive charge (like charges repel each other). Since like charges repel one another, the few positively charged α particles that changed paths abruptly must have hit, or closely approached, another body that also had a highly concentrated, positive charge. Since the deflections occurred a small fraction of the time, this charge only occupied a small amount of the space in the gold foil. Analyzing a series of such experiments in detail, Rutherford drew two conclusions: 1. The volume occupied by an atom must consist of a large amount of empty space 2. A small, relatively heavy, + charged body, the nucleus, must be at the center of each atom This analysis led Rutherford to propose a model in which an atom consists of a very small, positively charged nucleus, in which most of the mass of the atom is concentrated, surrounded by the negatively charged electrons, so that the atom is electrically neutral. After many more experiments, Rutherford also discovered that the nuclei of other elements contain the hydrogen nucleus as a "building block," and he named this more fundamental particle the proton, the positively charged, subatomic particle found in the nucleus. With one addition, which you will learn next, this nuclear model of the atom, proposed over a century ago, is still used today. The α particles are deflected only when they collide with or pass close to the much heavier, positively charged gold nucleus. Because the nucleus is very small compared to the size of an atom, very few α particles are deflected. Most pass through the relatively large region occupied by electrons, which are too light to deflect the rapidly moving particles.

atomic number

The number of protons in the nucleus of an atom is its atomic number (Z). This is the defining trait of an element: Its value determines the identity of the atom. For example, any atom that contains six protons is the element carbon and has the atomic number 6, regardless of how many neutrons or electrons it may have. A neutral atom must contain the same number of positive and negative charges, so the number of protons equals the number of electrons. Therefore, the atomic number also indicates the number of electrons in an atom.

mass spectrometry (MS)

The occurrence and natural abundances of isotopes can be experimentally determined using an instrument called a mass spectrometer. Mass spectrometry (MS) is widely used in chemistry, forensics, medicine, environmental science, and many other fields to analyze and help identify the substances in a sample of material. In a typical mass spectrometer (Figure 2.15), the sample is vaporized and exposed to a high-energy electron beam that causes the sample's atoms (or molecules) to become electrically charged, typically by losing one or more electrons. These cations then pass through a (variable) electric or magnetic field that deflects each cation's path to an extent that depends on both its mass and charge (similar to how the path of a large steel ball bearing rolling past a magnet is deflected to a lesser extent that that of a small steel BB). The ions are detected, and a plot of the relative number of ions generated versus their mass-to-charge ratios (a mass spectrum) is made. The height of each vertical feature or peak in a mass spectrum is proportional to the fraction of cations with the specified mass-to-charge ratio. Since its initial use during the development of modern atomic theory, MS has evolved to become a powerful tool for chemical analysis in a wide range of applications.

Summarize the findings of JJ Thomson.

The question existed, if matter is composed of atoms, what are the atoms composed of? Are they the smallest particles, or is there something smaller? In the late 1800s, a number of scientists interested in questions like these investigated the electrical discharges that could be produced in low-pressure gases, with the most significant discovery made by English physicist J.J. Thomson using a cathode ray tube. This apparatus consisted of a sealed glass tube from which almost all the air had been removed; the tube contained two metal electrodes. When high voltage was applied across the electrodes, a visible beam called a cathode ray appeared between them. This beam was deflected towards the positive charge and away from the negative charge, and was produced in the same way with identical properties when different metals were used for electrodes. In similar experiments, the ray was simultaneously deflected by an applied magnetic field, and the measurements of the extent of deflection and the magnetic field strength allowed thomson to calculate the charge-to-mass ratio of the cathode ray particles. The results of these measurements indicated that these particles were much lighter than atoms. Based on his observations, here is what Thomson proposed and why: the particles are attracted by positive (+) charges and repelled by negative (-) charges, so they must be negatively charged (like charges repel like and unlike charges attract); they are less massive than atoms and indistinguishable, regardless of the source material, so they must be fundamental, subatomic constituents of all atoms. Although controversial at the time, Thomson's idea was gradually accepted, and his cathode ray particle is what we now call an electron, a negatively charged, subatomic particle with a mass more than one thousand-times less that of an atom. The term "electron" was coined in 1891 by Irish physicist George Stoney, from "electric ion."

structural formula

The structural formula for a compound gives the same information as its molecular formula (the types and numbers of atoms in the molecule) but also shows how the atoms are connected in the molecule. The structural formula for methane contains symbols for one C atom and four H atoms, indicating the number of atoms in the molecule (Figure 2.16). The lines represent bonds that hold the atoms together. (A chemical bond is an attraction between atoms or ions that holds them together in a molecule or a crystal.) We will discuss chemical bonds and see how to predict the arrangement of atoms in a molecule later. For now, simply know that the lines are an indication of how the atoms are connected in a molecule. A ball-and-stick model shows the geometric arrangement of the atoms with atomic sizes not to scale, and a space-filling model shows the relative sizes of the atoms.

chemical symbol for isotopes

The symbol for a specific isotope of any element is written by placing the mass number as a superscript to the left of the element symbol (Figure 2.14). The atomic number is sometimes written as a subscript preceding the symbol, but since this number defines the element's identity, as does its symbol, it is often omitted. For example, magnesium exists as a mixture of three isotopes, each with an atomic number of 12 and with mass numbers of 24, 25, and 26, respectively. These isotopes can be identified as (superscripts) 24Mg, 25Mg, and 26Mg. These isotope symbols are read as "element, mass number" and can be symbolized consistent with this reading. For instance, 24Mg is read as "magnesium 24," and can be written as "magnesium-24" or "Mg-24." 25Mg is read as "magnesium 25," and can be written as "magnesium-25" or "Mg-25." All magnesium atoms have 12 protons in their nucleus. They differ only because a 24Mg atom has 12 neutrons in its nucleus, a 25Mg atom has 13 neutrons, and a 26Mg has 14 neutrons.

polyatomic ions

These ions, which act as discrete units, are electrically charged molecules (a group of bonded atoms with an overall charge).

properties of molecular compounds

We can often identify molecular compounds on the basis of their physical properties. Under normal conditions, molecular compounds often exist as gases, low-boiling liquids, and low-melting solids, although many important exceptions exist. Whereas ionic compounds are usually formed when a metal and a nonmetal combine, covalent compounds are usually formed by a combination of nonmetals While we can use the positions of a compound's elements in the periodic table to predict whether it is ionic or covalent at this point in our study of chemistry, you should be aware that this is a very simplistic approach that does not account for a number of interesting exceptions. Shades of gray exist between ionic and molecular compounds, and you'll learn more about those later.

ionic bonds

When electrons are transferred and ions form, ionic bonds result. Ionic bonds are electrostatic forces of attraction, that is, the attractive forces experienced between objects of opposite electrical charge (in this case, cations and anions).

properties of ionic compounds

You can often recognize ionic compounds because of their properties. Ionic compounds are solids that typically melt at high temperatures and boil at even higher temperatures. For example, sodium chloride melts at 801 °C and boils at 1413 °C. (As a comparison, the molecular compound water melts at 0 °C and boils at 100 °C.) In solid form, an ionic compound is not electrically conductive because its ions are unable to flow ("electricity" is the flow of charged particles). When molten, however, it can conduct electricity because its ions are able to move freely through the liquid (Figure 2.30). In every ionic compound, the total number of positive charges of the cations equals the total number of negative charges of the anions. Thus, ionic compounds are electrically neutral overall, even though they contain positive and negative ions. We can use this observation to help us write the formula of an ionic compound. The formula of an ionic compound must have a ratio of ions such that the numbers of positive and negative charges are equal.

Biomarkers

a measurable substance in an organism whose presence is indicative of some phenomenon such as disease, infection, or environmental exposure. Recent studies have shown that your exhaled breath can contain molecules that may be biomarkers for recent exposure to environmental contaminants or for pathological conditions ranging from asthma to lung cancer. Scientists are working to develop biomarker "fingerprints" that could be used to diagnose a specific disease based on the amounts and identities of certain molecules in a patient's exhaled breath.

law of definite proportions

aka law of constant composition Dalton knew of the experiments of French chemist Joseph Proust, who demonstrated that all samples of a pure compound contain the same elements in the same proportion by mass. This statement is known as the law of definite proportions. For ex, when different samples of isooctane (a component of gasoline and one of the standards used in the octane rating system) are analyzed, they are found to have a carbon-to-hydrogen mass ratio of 5.33:1 It is worth noting that although all samples of a particular compound have the same mass ratio, the converse is not true in general. That is, samples that have the same mass ratio are not necessarily the same substance. For example, there are many compounds other than isooctane that also have a carbon-to-hydrogen mass ratio of 5.33:1.00.

example of law of multiple proportions with Cu and Cl:

copper and chlorine can form a green, crystalline solid with a mass ratio of 0.558 g chlorine to 1 g copper, as well as a brown crystalline solid with a mass ratio of 1.116 g chlorine to 1 g copper. These ratios by themselves may not seem particularly interesting or informative; however, if we take a ratio of these ratios, we obtain a useful and possibly surprising result: a small, whole-number ratio. This 2-to-1 ratio means that the brown compound has twice the amount of chlorine per amount of copper as the green compound. This can be explained by atomic theory if the copper-to-chlorine ratio in the brown compound is 1 copper atom to 2 chlorine atoms, and the ratio in the green compound is 1 copper atom to 1 chlorine atom. The ratio of chlorine atoms (and thus the ratio of their masses) is therefore 2 to 1 (Figure 2.5).