CHEM 110 Ch.2 Atoms, Molecules, and Ions

ionic hydrate prefixes

1 (sometimes omitted): mono- 2: di- 3: tri- 4: tetra- 5: penta- 6: hexa- 7: hepta- 8: octa- 9: nona- 10: deca-

The Postulates of Dalton's 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 (Figure 2.2). A macroscopic sample of an element contains an incredibly large number 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 atoms 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 are always present in the same ratio (Figure 2.3). 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 (Figure 2.4).

ionic compounds

A compound that contains ions and is held together by ionic bonds. When a metal is combined with one or more nonmetals, the compound is usually ionic.

structural isomers

Acetic acid and methyl formate are structural isomers, compounds in which the molecules differ in how the atoms are connected to each other.

Anion (negative ion)

An atom that gains one or more electrons will exhibit a negative charge and is called an anion. -Example, 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 --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−).

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. example: 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

Compounds Containing Polyatomic Ions

Compounds containing polyatomic ions are named similarly to those containing only monatomic ions, i.e. by naming first the cation (metal) and then the anion (non-metal). examples:KC2H3O2, potassium acetate NH4Cl, ammonium chloride NaHCO3, sodium bicarbonate CaSO4, calcium sulfate Al2(CO3)3, aluminum carbonate Mg3(PO4)2, magnesium phosphate

Gold Foil Experiment

He performed a series of experiments using a beam of high-speed, positively charged alpha particles (α particles) that were produced by the radioactive decay of radium; α particles consist of two protons and two neutrons. -Rutherford and his colleagues Hans Geiger (later famous for the Geiger counter) and Ernest Marsden aimed a beam of α particles, the source of 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 α particles using a luminescent screen that glowed briefly where hit by an α particle. What did they discover? Most particles passed right through the foil without being deflected at all. However, some were diverted slightly, and a very small number were deflected almost 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, positively 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 (Figure 2.10). 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.

binary acid

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 examples: HF(g), hydrogen fluoride HF(aq), hydrofluoric acid HCl(g), hydrogen chloride HCl(aq), hydrochloric acid HBr(g), hydrogen bromide HBr(aq), hydrobromic acid HI(g), hydrogen iodide HI(aq), hydroiodic acid H2S(g), hydrogen sulfide H2S(aq), hydrosulfuric acid

Plum Pudding Model and Saturn Model of a proton

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

ionic hydrates

Ionic compounds that contain water molecules as integral components of their crystals examples: copper(II) sulfate pentahydrate CuSO4 ∙5H2 O sodium carbonate decahydrate Na2 CO3 ∙10H2 O

a subscript following a symbol vs a number in front of a symbol

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.

Atom, protons, neutrons, electrons

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.

Millikan's Oil Drop Experiment

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 individual drops. Looking at the charge data that Millikan gathered, you may have recognized that the charge of an oil droplet is always a multiple of a specific charge, 1.6 × 10−19 C. Millikan concluded that this value must therefore be a fundamental charge—the charge of a single electron

Cation (positive ion)

Positively charged atoms called cations are formed when an atom loses one or more electrons. 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+).

covalent/molecular compounds

Result when atoms share, rather than transfer (gain or lose), electrons. Covalent compounds are usually formed by a combination of nonmetals. -Under normal conditions, molecular compounds often exist as gases, low-boiling liquids, and low-melting solids, although many important exceptions exist.

Compounds Containing Only Monatomic 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) example: NaCl, sodium chloride Na2O, sodium oxide KBr, potassium bromide CdS, cadmium sulfide CaI2, calcium iodide Mg3N2, magnesium nitride CsF, cesium fluoride Ca3P2, calcium phosphide LiCl, lithium chloride Al4C3, aluminum carbide

naming covalent compounds

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 examples: SO2: sulfur dioxide BCl3: boron trichloride SO3: sulfur trioxide SF6: sulfur hexafluoride NO2: nitrogen dioxide PF5: phosphorus pentafluoride N2O4: dinitrogen tetroxide P4O10: tetraphosphorus decaoxide N2O5: dinitrogen pentoxide IF7: iodine heptafluoride

atomic number (Z)

The number of protons in the nucleus of an atom. The atomic number also indicates the number of electrons in an atom. -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.

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

mass number (A)

The total number of protons and neutrons in an atom -The number of neutrons is therefore the difference between the mass number mass # - atomic # = # of neutrons A=Z+N

naming oxyacids

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" EXAMPLES: Formula:HC2H3O2 Anion Name: acetate Acid Name: acetic acid Formula:HNO3 Anion Name: nitrate Acid Name: nitric acid HNO2 nitrite nitrous acid HClO4 perchlorate perchloric acid H2CO3 carbonate carbonic acid H2SO4 sulfate sulfuric acid H2SO3 sulfite sulfurous acid H3PO4 phosphate phosphoric acid

(amu), (e), (Da)

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) -one amu is exactly 1 of the mass of one carbon atom: 1 amu = 1.6605 × 10^-24 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

covalent/molecular bonds

When electrons are "shared" and molecules form. 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.

ionic bond

When electrons are transferred and ions form. 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)

empirical formula

a chemical formula showing the ratio of elements in a compound rather than the total number of atoms -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.

molecular formula

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. -Molecular formulas are also used as abbreviations for the names of compounds. -example: C6H12O6

The law of definite proportions or The law of constant composition

all samples of a pure compound contain the same elements in the same proportion by mass Example: 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. 14.82 g carbon/2.78 g hydrogen = 5.33 g carbon/1.00 g hydrogen 22.33 g carbon/4.19 g hydrogen = 5.33 g carbon/1.00 g hydrogen

chemical symbol

an abbreviation that we use to indicate an element or an atom of an element. For example, the symbol for mercury is Hg

Isotopes

atoms of the same element that differ in mass. -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. -The existence of the neutron also explained isotopes: They differ in mass because they have different numbers of neutrons, but they are chemically identical because they have the same number of protons. -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 (These isotopes can be identified as 24^Mg, 25^Mg, and 26^Mg, 24^Mg is read as "magnesium 24," and can be written as "magnesium-24" or "Mg-24.") All magnesium atoms have 12 protons in their nucleus. They differ only because a 24^Mg atom has 12 neutrons in its nucleus, a 25^Mg atom has 13 neutrons, and a 26^Mg has 14 neutrons.

spatial isomers

compounds in which the relative orientations of the atoms in space differ 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.

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

Isomers

compounds with the same chemical formula but different molecular structures example: Methyl formate molecules have one of the oxygen atoms between the two carbon atoms, differing from the arrangement in acetic acid molecules. -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.

electron

his cathode ray particle is what we now call an ________, 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."

monatomic ions

ions formed from a single atom

acid

many acids release hydrogen ions, H+, when dissolved in water

metalloids

metalloids: elements that conduct heat and electricity moderately well and possess some properties of metals and some properties of nonmetals

metals

metals: elements that are shiny, malleable, good conductors of heat and electricity

nonmetals

nonmetals: elements that appear dull, poor conductors of heat and electricity

The law of multiple proportions

states that when two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small, whole numbers. For example, 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. (1.116 g Cl/1 g Cu)/(0.558 g Cl/1 g Cu)= 2/1 -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

Compounds Containing a Metal Ion with a Variable Charge

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+ 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.

periodic law

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

polyatomic ion

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

binary compounds

those containing only two elements

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 because they have the same number of protons.