Chemistry chapter 2

The atomic theory

2.1. The atomic theory • elements are composed of extremely small particles called Atoms • all atoms of a given element are identical, having the same size, mass and chemical properties. The atoms of one element are different from the Atoms of all other elements. • Compounds are composed of atoms of any two of the elements present in either an integer or a small fraction. • A chemical reaction involves only the separation, combination or rearrangement of atoms, it does not result in their creation or destruction

Molecules

5 molecules and ions Molecules • a molecule is an aggregated of at least two atoms in a definite arrangement held together by chemical forces (also called chemical bonds). • A molecule may contain atoms of the same element or atoms of two or more elements joined in a fixed ratio in accordance with the law of definite proportion stated in section 2.1 • thus, a molecule is not necessarily a compound, which by definition is made up of two or more elements. • Hydrogen gas, for example, is a pure element, but it can consists of molecules made up of two hydrogen atoms, each. • Water on the other hand, is a molecular compound that contains hydrogen and oxygen in a ratio of two hydrogen atoms and one oxygen atoms • like atoms, molecules are electrically neutral

A molecular formula

A molecular formula • shows the exact number of atoms of each element in the smallest unit of a substance (or How many of each element Is in the molecule) • (ex water the subscript 2 is mixed with hydrogen . There is nothing being mixed with oxygen. There's two hydrogens and one oxygen in the molecule. • (in our discussion of molecules, each example was given with its molecular formula in parentheses) • Thus h2 is the molecular formula for hydrogen 02 is oxygen03 is ozonezone and h20 is water • the subscript. Indicates the number of atoms of an element present. There is no subscript for o in the h20 , because there is only one atom of oxygen in a molecule of water, and so the number one is omitted from the formula. Note that oxygen and O zone are Allah tropes of oxygen

Allotrope

Allotrope • is one of two or more distinct forms of an element. • Two allotrope forms of the element carbon - diamond and graphite - are dramatically different. Not only in properties but also in their relative cost.

Monatomic ions

An atom can lose or gain more than one electron. Examples of ions form by the loss or gain of more than one electron are MG^2+,FE^3,S^2 and N^3. These ions as well as NA+ and Cl- are called Monaatomic ions because Monatomic ions • they contain only one atom. Figure .211 shows the charges of a number of Monatomic ion • with very few exceptions metals tend to form catons and nonmetals form anions in addition 2 more atoms can combine to form an ion that has a net positive or net negative charge

Atomic number Z

Atomic number Z • is the number of protons in the nucleus of each atom of an element • in a neutral atom the number of protons is equal to the number of electrons, so the atomic number also indicates the number of electrons present in the atom. The chemical identity of an atom can be determined solely from its atomic number . o For example, the atomic number of Flouorine is nine. This means that each fluorine atom has nine protons and nine electrons o viewed another way, every atom in the universe that contains nine protons is correctly named flouorine.

bROMIDE

Br-

Chlorate

CLO /3-

Carbonate

CO 2/3-

dICHROMATE

CR202/7-

Chromate

CRO 2/4-

cesium

CS+

cation anion

Cations • the loss of one or more electrons from a neutral atom results in a cation • an ion with a positive charge • for example, a sodium atom can readily lose an electron to become a sodium cation, which is represented by NA+ • cations can be found in group 1a elements and 2a elements also aluminum and Gallium Anion • is an ion pulls net charge is negative due to an increase in the number of electrons. A chlorine atom, for instance, can gain an electron to become the chlorideing ion CL- • group 7a, also nitrogen, oxygen • if you take a plus sodium and A- chlorine= you will get a neutral sodium chloride Sodium chloride ordinary table salt is called an ionic compound because it is formed from caction and Anion.

Chemical formulas

Chemical formulas • chemist used chemical formulas to express the composition of molecules and ionic compounds in terms of chemical symbols.(In other words, they are elements with subscripts only ex water is one ) By composition, we mean not only the element present but also the ratio in which the atoms are combined. We are concerned with two types of formulas. • Molecular formulas and empirical formulas

chloride

Cl-

cathode ray tube was the device use to investigate atomic structure. radiation

Electrons in 1890s, many scientists became caught up in the study of radiation • radiation is the admission and transmission of energy through space in the form of waves. o Information gained from this research contributed greatly to our understanding of atomic structure o one device use to investigate this phenomenon was a cathode ray tube cathode ray tube • it was the forerunner of the television. It is the glass tube from which most of the air has been evacuated. When the two metal plates are connected to a high-voltage source. The negatively charged plate called the cathode admits an invisible Ray. The cathode Ray is drawn to the positively charged plate called the anode, where it passes through a hole and continues traveling to the other side of the tube. When the ray strikes the special coded surface to produce a strong fluorescent or bright light. See page 41 because the cathode Ray is attracted by the plate bearing positive charges and repels by plate bearing a negative charge, it must consist of negative charge particles we know that these negatively charged particles as electrons.

Electrons what are the mass and charge of an electron JJ Thomson do? Robert Millikan do?

Electrons • negatively charged particles an English physicists JJ Thomson use a C ray tube and his knowledge of electromagnet. To determine the ratio of electric charge to the mass of an individual electron. The number he came up with was -1.76×10 to 8 power c/g , where c stands for column, which is the unit of electric charge. Robert Millikan Thereafter, in a series of experiments carried out between 1908 and 1917 Robert Millikan succeeded in measuring the charge of the electron with great precision. His work provided that the charge of each electron was exactly the same. In his experiment. He examined the motion of single tiny drops of oil that picked up static charge from ions in the air. He suspended the charge drop in the air By applying an electric field and followed their motion through a microscope using his knowledge of electrostatics, he found the charge of an electron to be -1.6022×10 ^ -19c from these data, he calculated the mass of it and electron see page 2.4. The mass of an electron equals 9.10×10 ^-28 g e- charge = -1.60 x 10^-19 C Thomson's charge/mass of e- = -1.76 x 10^8 C/g e- mass = 9.10 x 10^-28 g

Empirical formulas

Empirical formulas • An empirical formula shows the simplest whole-number ratio of the atoms in a substance • the molecular formula of hydrogen peroxide, a substance used as an antiseptic and as a bleaching agent for textiles and hair is H2o2. This formula indicates that each hydrogen peroxide molecule consists of two hydrogen atoms and two oxygen atoms. The ratio of hydrogen to oxygen atoms in the molecule is 2:2 or 1:1. • The empirical formula of hydrogen peroxide is H0. • Thus , the empirical formula tells such which element are present, and the simplest whole number ratio of their atoms, but not necessarily the actual number of atoms in a given molecule. • Another example, consider the compound hydrazine (seepg53), which is used as a rocket fuel. The empirical formula of hydrazine is nH2. Although the ratio of nitrogen to hydrogen is 1:2 in both of the molecular formulas and the empirical formula (see text). Only the molecular formula tells us the actual number of nitrogen atoms and hydrogen atoms present in hydrazine molecule • See text • Empirical formulas are the simplest chemical formulas they are written by reducing the subscripts in the molecular formulas to the smallest possible whole number. Molecular formulas are the true formulas of molecules. If we know the molecular formula. We also note the empirical formula, but the reverse is not true. • Chemist can misuse empirical formulas because when a chemist, analyze and unknown compound. The first step is usually the determination of the compound empirical formula. With additional info, it is possible to deduce the molecular formula. • Four. Many molecules the molecular formula and the empirical formula or one and the same. Some examples are water, ammonia, carbon dioxide and methane

metal nonmetal metaloid

Everything else is called representative metals • a metal- is a good conductor of heat and electricity • nonmetal- is usually a poor conductor of heat and electricity • metalloid-has properties that are intermediate between those of metals and nonmetals(sometime acts like metals and nonmetals it act like metals in certain conditions). o Figure 2.10 shows that the majority of known elements are metals, only 17 elements are nonmetals and eight elements are metalloids. From left to right across any period, the physical and chemical properties of the elements change gradually from metallic to nonmetallic

DIHYDROGEN PHOSPHATE

H2P04-

HYDROGEN CARBONATE

HCO-3

HYDROXIDE

HO-

HYDROGEN PHOSPHATE

HPO2/4

HYDROGEN SULFATE

HSO-4

mercury

Hg 2/2

ions

Ions • an ion is an atom or a group of atoms that has a net positive or negative charge. • The number of positively charged protons in the nucleus of an atom remains the same. During ordinary chemical changes (called chemical reaction), but negatively charged electrons may be lost or gained.

Isotopes

Isotopes • atoms that have the same atomic number, but different mass number • for example, there are three isotopes of hydrogen. One simply known as hydrogen has one proton and no neutron. • The deuterium isotope contains one proton and one neutron and tritium has one proton and 2 neutrons. The accepted way to denote the atomic number and mass of an atom of an element (x) is as follows See pg 46 (the isotope changes the mass of the nucleus, so you have to consider the number of neutrons in the system when you consider a isotope. There is a hydrogen with 2 nucleons in it (deuterium, and there is one with 3 which is tritium the atomic number makes them apart of the same family. Hydrogen- it has one proton and zero neutrons The deteutron-has one proton and one neutron The tritium has one proton and two neutron Different elements can have different isotopes will have the same number of protons but the size of the nucleus will be bigger) There are some advantages to that because it is still hydrogen, but still have the chemical characteristics of hydrogen, but because of the mass difference. You can use it to study compounds if the compound goes into a reaction in some of the bonds are broke see pic in book the isotope systems are sometime used in Connecticut, labeling other type of isotopes are carbon 12, carbon 13, carbon 14 • as another example, consider two common isotopes of uranium with mass numbers of 235 and 238, respectively • the first isotope uranium 235 is used in nuclear reactors and atomic bombs, whereas the second isotopes , uranium 238 lacks the properties necessary for these applications. With the exceptions of hydrogen, which has different names for each of its isotopes, isotopes of elements are identified by their mass numbers. thus the preceding two isotopes are called uranium - 235 and uranium - 238 • the chemical properties of an element are determined primarily by the protons and electrons in its atoms, neutrons do not take part in chemical changes under normal conditions. Therefore, isotopes of the same element have similar chemistry, forming the same type of compounds and displaying similar reactivity's example 2.1 shows how to calculate the number of protons, neutrons and electrons using atomic number and mass number • see how to calculate number of protons, neutrons and electrons using atomic number and mass number on page 47

Lithium

Li+

PERMANGANATE

MNO4

Mass number A

Mass number A • is the total number of neutrons and protons present in the nucleus of an atom of an element. • Except for the most common form of hydrogen, which has one proton and no neutron, all atomic nuclei contain both protons and neutrons. In general, the mass number is given by the number of neutrons in an atom is equal to the difference between the mass number and the atomic number or A-Z o for example, if the mass number of a particle barron atom is 12 and atomic number is five (indicating five protons in the nucleus), then the number of neutrons is 12-5 = 7. Note that all three quantities (atomic number, number of neutrons and mass number) must be positive integers or whole numbers. o This symbol is useful to distinguish whether you have a neutral system or a isotope • mass number= number of protons + number of neutrons • = atomic number + number of neutrons

Molecular models ball and stick Space filling models

Molecular models molecules are too small for us to observe directly. An effective means of visualizing them is by the use of molecular models two. Standard type of molecular models are currently in use • ball and stick models and space filling models ball and stick • the atoms are wooden or plastic balls with holes in them. Sticks or springs are used to represent chemical bonds. The angles they form between atoms. Approximate the bond angle in actual molecules with the exception of the H atom. The ball are all the same size and each type of atom is represented by a specific color. Space filling models • atoms are represented by truncated balls held together by snaps, fastener is so that the bonds are not visible. The ball are proportional in size to atoms structural formula • the first step towards building a molecular model is writing the structural formula which shows how atoms are bonded to one another in a molecule. • For example, it is known that each of the two H atoms is bonded to an O atom in the water molecule. Therefore, the structural formula of water is H-0-H. a line connecting the two atomic symbol represents a chemical bond ball and stick models showed the three-dimensional arrangement of atoms. Clearly, and they are fairly easy to construct. However, the balls are not proportional to the size of atoms. Furthermore, the sticks greatly exert gate. The space between atoms in a molecule. Space filling models are more accurate because they show the variation in atomic size. The drawbacks are that they are time-consuming to put together and they do not show the three-dimensional positions of atoms very well.

ammonium

NH+ 4

NITRITE NITRIDE

NO2 N^3

NITRATE

NO3

sodium

Na+

OXIDE

O2-

PEROXIDE

O2/2

PHOSPHATE

PO3/4

Polyatomic ions

Polyatomic ions • such as hydrogen ion, cyanide ion and ammonium ion containing more than one atom

define Radioactivity and the 3 rays

Radioactivity • in 1895, the German Rontgen physicist William notice that the cathode rays cause glass and metal to admit very unusual rains. This highly energetic radiation penetrated matter, dark in covered photographic plates and caused a variety of substances to Florence. Because those rays could not be deflected by a magnet, they could not contain charged particles as cathode rays do. Rontgen called them x-rays because their nature was not known • not long after rontgen discovered, Antonio, a professor of physics in Paris began to study the fluorescent properties of substances. Purely by accident, he found that exposing thickly wrapped photographic plates to a certain uranium compound caused them to darken even without the simulation of the cathode rays. Like x-rays. The rays from the uranium compound were highly energetic and could not be deflected by a magnet, but they deferred from x-rays because they aroused spontaneously. One of Antonio students Maria suggest the name radioactivity o radioactivity-to describe the spontaneous emission of particle and or radiation. Since then, any element that spontaneously emits radiation is said to be radioactive three types of rays are produced by the decay or breakdown of radioactivity substance such as uranium two of the three are deflected by opposite charged plate. • Alpha rays consists of positively charged particles called a particles and therefore are deflected by the positively charged plate. • Beta rays or B particles are electrons and are deflected by the negatively charged plate • Gama rays-the third of radioactive radiation consists of high energy rays call gamma rays. Like x-rays y rays have no charge and are not affected by an external field

SULFIDE

S2

THIOCYANATE

SCN-

SULFITE

SO2/3

SULFATE

SO2/4

The law of conservation of masses

The law of conservation of masses which is that matter can be neither created nor destroyed, only changed. Because matter is made of atoms and are unchanged in chemical reactions, it follows that mass must be conserved as well.

The neutron Neutrons , because they proved to be electrically neutral particles having a mass slightly greater than that of protons

The neutron • Rutherford model of atomic structure left one major problem unsolved • it was known that hydrogen. The simplest atom contains only one proton and that the helium atom contains two protons • therefore, the ratio of the mass of a helium atom to that of a hydrogen atom should be 2:1(because electrons are much lighter than protons, their contribution to a atomic mass can be ignored. In reality, however, the ratio is 4:1 • ruthford and others poststulated that there must be another type of subatomic particle in the atomic nucleus, the proof was provided by another English physicist James in 1932, when James bombarded a thin sheet of beryllium with a particles in very high energy radiation. Similarly to y rays was admitted by the metal. Later experiment showed that the rays actually consisted of a third type of subatomic particles which James named neutrons . • • the mystery of the mass ratio could now be explained in the helium nucleus. There are two protons and two neutrons, but in the hydrogen nucleus. There is only one proton and no neutron, therefore, the ratio is 4:1 • figure 2.9 shows the location of the elementary particle (protons, neutrons and electrons) in an atom. There are other subatomic particles, but the electron, the proton and the neutron are three fundamental components of the atom that are important in chemistry. Table 2.1 shows the masses and charges of these three elementary particles

The structure of the atom

The structure of the atom on the basis of D atomic theory, we can define an atom-- as the basic unit of an element that can enter into chemical combination atoms are made up of small particles called subatomic particles which are electrons, protons and neutrons

atomic number, mass number and isotopes

atomic number, mass number and isotopes all atoms can be identified by the number of protons and neutrons. They contain

atoms

atoms • at this stage of investigation, scientist, perceived the atoms as follows o the mass of a nucleus constitute most of the mass of the entire Atom o but the nucleus occupies only about 1/10^13 of the volume of the atom o we express atomic (and molecular) dimensions in term of the SI unit called the picometer(pm) where 1PM=1x10^-12m o a typical atomic radius is about 100pm o where as the radius of an atomic nucleus is only about 5x10^-3 pm the mass of the proton is 1840 times the mass of the electron the volume of the nucleus with respect to the Atom is 1/10^-13 to the atom the nucleus has the protons, neutrons and electrons • the protons and neutrons and electrons live inside the nucleus. The electron is outside the nucleus an atom is one pekometer the diameter of an atom is one akstrum the neutron

diatomic molecule

diatomic molecule, single atoms are called mono atomic items • the hydrogen molecules symbolize as H2 is called a diatomic molecule. Because it contains only two atoms diatomic molecule contains only 2 atoms • other elements that normally exists as diatomic molecule are nitrogen and oxygen as well as the group 7a elements , fluorine, chlorine, bromine, and iodine. • Of course, a diatomic molecule can contain atoms of different elements. • Examples are hydrogen chloride and carbon monoxide. The vast majority of molecules contain more than two atoms. They can be atoms of the same element as in O zone, which is made up of three atoms of oxygen or they can be combinations of two or more different elements Polyatomic molecules • molecules containing more than two atoms. Like ozone water and ammonia are polyatomic molecules.

formula of ionic compounds

formula of ionic compounds ionic compounds consist of a combination of cations and an anions • The formula is usually the same as the empirical formula • because ionic compounds do not consist of discrete molecular units. For example, a solid sample of sodium chloride consists of equal number of sodium and chloride ions arranged in a three-dimensional network. In such a compound there is a one-to-one ratio of cations to anions so that the compound is electrically neutral • The sum of the charges on the cation(s) and anion(s) in each formula unit must equal zero (see pg 54) For ionic compound to be electrically neutral the sum of the charges on the cationic and an ion each formula unit must be zero. If the charges on the cationic and anion are numerically different we apply the following rule to make the formula electrically neutral • the subscript of the cationic is numerically equal to the charge on the anionic and the subscript of the anion is numerically equal to the charge on the cation. If the charges are numerically equal, then no subscript are necessary. This rule follows from the fact that because the formula of ionic compounds are usually empirical formulas. The subscript must always be reduced to the smallest ratio see example on page 55 example sodium exists as a + one charge and chlorine exists as a - charge. The way to write this formula is to take the charges and write subscripts for them. Since the cation and anion will neutralize you take the number from the cation and make it the subscript of the anion and the number for the anion and put it to the subscript of the anion and then you'll get Nacl see pg 55 for example of the more complicated problems aluminum oxidize- al is +3 , oxygen is-2 • you cat ion and make it the subscript of the and ion and ion and make the subscript of the cat ion. See pic in example • therefore, you write it as Al2o3

mercuric

hg2+

law of definite proportions

law of definite proportions states that different samples of the same compound always contain its constitute elements in the same proportion by mass. Thus, if we were to analyze samples of carbon dioxide gas obtained from different sources, we would find in each sample the same ratio of mass of carbon to oxygen. It stands to reason that if the ratio of the masses of different elements in a given compound is fixed, the ratio of the atoms of these elements in the compound also must be constant The law of definite proportions is a law of science that says that a chemical compound is always made up of the exact same proportion of elements by mass. So, if a compound is made by combining 1/4 from one chemical and the remaining 3/4 from another chemical, these proportions will always hold true, regardless of the amount of chemicals added. The Law of Definite of Proportions is sometimes referred to as Proust's Law because it was originally observed by a French chemist named Joseph Proust. In the modern world, this law seems obvious, but in Proust's day it was a new idea, because some scientists thought that any combinations of elements could make certain substances, rather than the substance needing to be created by a definite proportion. Common Examples of the Law of Definite Proportions Water, written as the chemical compound H20, is made up of atoms of hydrogen and oxygen. If one oxygen atom is combined with two hydrogen atoms, water is created. An oxygen atom has an atomic mass of 16, while a hydrogen atom has an atomic mass of 1. This means that water is made up of 11% hydrogen and 89% oxygen. The exact same proportion of hydrogen and oxygen must always be combined in order for water to be created. Water could never be created by combining a ratio of 20% hydrogen and 80% oxygen, because the proportions are not correct; a different chemical compound would be created by mixing this ratio. The law of definite proportions is a law of science that says that a chemical compound is always made up of the exact same proportion of elements by mass. So, if a compound is made by combining 1/4 from one chemical and the remaining 3/4 from another chemical, these proportions will always hold true, regardless of the amount of chemicals added. The Law of Definite of Proportions is sometimes referred to as Proust's Law because it was originally observed by a French chemist named Joseph Proust. In the modern world, this law seems obvious, but in Proust's day it was a new idea, because some scientists thought that any combinations of elements could make certain substances, rather than the substance needing to be created by a definite proportion. Common Examples of the Law of Definite Proportions Water, written as the chemical compound H20, is made up of atoms of hydrogen and oxygen. If one oxygen atom is combined with two hydrogen atoms, water is created. An oxygen atom has an atomic mass of 16, while a hydrogen atom has an atomic mass of 1. This means that water is made up of 11% hydrogen and 89% oxygen. The exact same proportion of hydrogen and oxygen must always be combined in order for water to be created. Water could never be created by combining a ratio of 20% hydrogen and 80% oxygen, because the proportions are not correct; a different chemical compound would be created by mixing this ratio. Salt, written as the chemical compound NaCl, is made up of atoms of Sodium (Na) and Chlorine (Cl). The exact same proportions of sodium and chlorine must always be combined in order for salt to be created. Sulfuric acid is made up of the individual elements of hydrogen, sulphur, and oxygen. The chemical compound is written H2SO4. The same proportions of hydrogen, sulphur, and oxygen must be combined to create sulfuric acid.

periodic table periods groups transitional metals

periodic table • a chart in which elements having similar chemical and physical properties are grouped together o PERIODS-the modern periodic table in which the elements are arranged by atomic number in horizontal rows o GROUPS-when arranged in a vertical column. They are known as groups or families o according to similarities in their chemical properties. Note that element 113 - 118, have recently been synthesize, although they have not yet been named the elements can be divided into three categories metals, nonmetals and metalloids transitional metals-The transition metals are the metallic elements that serve as a bridge, or transition, between the two sides of the table.

the law of multiple proportion

the law of multiple proportion according to the law. If two elements can combine to form more than one compound the masses of one element that combined with a fixed mass of the other element are in ratios of small whole numbers. (The law multiple proportions state that I can take the same two elements carbon and oxygen proportions and apply what ratios they appear, such as definite proportions, water would always be one oxygen and two hydrogen multiple ports and states that you can take any two elements to make a compound interest walked proportions to change the property if I put carbon and oxygen into all the one-to-one ratio, it will behave like carbon dioxide if I put a wanted to ratio will get carbon monoxide.(If I do a 2 to 1 ratio. I get hydrogen peroxide for delay one-to-one ratio I get water) (you take the same elements and dependent on the ratios you can combine them and make different elements) take two samples sample one and sample 2. If in sample one I want to use water and carbon dioxide in the same in sample 2. If I measure my compound in sample one in my compound and sample 2 I will always see this h20 what this law states is that if you define a compound in a definite proportion to each other every time we see one oxygen. With hydrogen attached to it. You always define that as water wherever you see this, it will still hold its properties as water, if you see it in sample three combined with blood or combined with methane as long there is H2O it will maintain its water as long as there's two hydrogen combine with oxygen. Whenever you see water. There's two hydrogen one oxygen wherever you see, carbon, there's two oxygen and one carbon

the protons and the nucleus what is the mass of a proton Ernest Rutherford discovered what?

the protons and the nucleus • by the early 1900s two features of atoms have become clear. They contain electrons and they are electrically neutral. To maintain electric neutrality an atom must contain an equal number of positive and negative charges. Therefore, Thompson proposed that an atom could be thought of as uniformed positive sphere of matter in which electrons are embedded like raisins in a cake. See figure 2.7. This so-called Plum pudding model was the perceptive theory for a number of years. Ernest Rutherford • In 1910, the New Zealand scientists Ernest Rutherford, who has studied with Thomas at Cambridge University, decided to use a particle to probe the structure of atoms. Together with his associate Hans and an undergraduate name Ernest marsden, Woodford carried out a series of experiments using very thin foils of gold and other metals as target for a particles from a radioactive source see figure 2.8. They observe that the majority of particles penetrated the foil either undeflected or with only a slight deflection. But every now and then and (a) particle was scattered (or deflected) at large angle. In some instances, and (A) particle actually bounced back in the direction from which it had come. This was a most surprising finding for in Thompson model the positive charge of the Atom was so diffused that the positive (A) particle should have passed through the foil with very little deflection. • Rutford was later able to explain the results of that (A) scattering experiment in terms of a new model for the Atom • Routford states that most of the atom must be empty space. This explains why the majority of (A) particles pass through the gold foil with little or no deflection. • The atoms positive charges routford proposed are all concentrated in the nucleus, which is a dense central core with the Atom • whenever an a particle came close to a nucleus in the scattering experiment, it experienced a large repulsive force and therefore a large deflection. • Moreover, an a particle traveling directly towards a nucleus would be completely repelled and its direction would be reversed. Protons • The positive charge particle in the nucleus are called protons • in separate experiments. It was found that each proton carried the same quantity of charges as an electron and has a mass of 1.67262 x 10^-24g about 1840 times the mass of the oppositely charged electron atoms positive charge is concentrated in the nucleus proton (p) has opposite (+) charge of electron (-) mass of p is 1840 x mass of e- (1.67 x 10-24 g)

This symbol is useful in identifying neutral and isotope Neutral • number of electrons equals number of protons • if you don't have a neutral you have a cation which is positively charge or a anion which is negatively charged (see ion notes) • see table

• Neutral means you have the same number of protons and say number of electrons • if you have something that is positively charge that means you have to have more protons than electrons 4-3=1 so that will be your cation in the next scenario you have three protons and four electrons so you have a anion • if you have a anion , it means you have more electrons in your system • your shifting the number of protons and electrons to form ions the atomic number is the number of protons. There are certain number of protons, neutral neutrons and electrons. If you know that a atom is neutral neutral atoms mean that the number of protons is the same as the number of electrons when you look at the periodic table, you assume that everything is neutral. They need to only give ,you one of these numbers either protons and electrons and you know what the other one is, they give you a certain amount of protons, then you know how many electrons you have,. If a atom is not neutral. They are usually called ions neutral ions you'll either get a plus charge or a minus charge. If you get get plus charge that means that some electrons left, leaving you with more protons. If you have a minus charge that means some electrons got added, leaving you with a negative. Atomic number atomic mass- is the total number of neutrons and protons presented in the nucleus of an atom of an element . See periodic table protons plus neutrons is the atomic mass (if all of the numbers on the periodic table are neutral. If you know all of the number of protons will be the same. As the number of electrons because the protons have a positive charge and electrons have a negative charge) Atoms of given element do not have the same mass. Most elements have two or more isotopes

elements are often referred to collectively by their periodic table group number (group 1A, group 2a and so on). However, for convenience, some element groups have been given special names group 1a group 2a group 7a group 8a

• The group 1, a elements (LI,NA.k,Rb,Cs anf Fr) are called alkali metals, and the group 2a elements)Be,mg,ca,sr,ba and ra) are called alkaline earth metals. • Elements in group 7, a ((F,Cl,Br,I and at) are known as halogens • and elements in group 8a(He,Ne,Ar,kr,xe and Rn) are called noble gases or rear gases