TENTH EDITION

GENERAL CHEMISTRYPrinciples and Modern Applications

PETRUCCI HERRING MADURA BISSONNETTE

Atoms and the Atomic Theory 2

PHILIP DUTTONUNIVERSITY OF WINDSOR

DEPARTMENT OF CHEMISTRY AND BIOCHEMISTRY

Atoms and the Atomic Theory

CONTENTS

2-1 Early Chemical Discoveries and the Atomic Theory

2-2 Electrons and Other Discoveries in Atomic Physics

2-3 The Nuclear Atom

2-4 Chemical Elements

2-5 Atomic Mass

2-6 Introduction to the Periodic Table

2-7 The Concept of the Mole and the Avogadro Constant

2-8 Using the Mole Concept in Calculations

2-1 Early Discoveries and the Atomic Theory

Lavoisier 1774 Formulate the law of conservation of

mass

He heated a sealed glass vessel containing a sample of tin and

some air

The mass before heating (vessel + tin + air)=after heating (vessel +

tin + air)

The total mass of the substance present after a chemical

reaction is the same as the total mass of substance before

the reaction.

Mass is conserved during a chemical reaction

FIGURE 2-2

Figure show the reaction between

silver nitrate and potassium

chromate to give a red solid (silver

chromate)

(a) Before the reaction, the beaker

with a silver nitrate solution and a

graduated potassium chromate

solution are placed on a single pan

balance displace the combine mass

= 104.5 g

(b) After mixing, a chemical reaction

occurs that forms silver chromate

(red precipitate) in potassium

nitrate solution. The total mass =

104.5 g, remains unchanged.

The low of conversation of mass says that matter is neither created nor destroyed in a chemical reaction

Proust 1799 Law of constant composition

All sample of the compound have the same composition- the same

proportions by mass of the constituent elements. Consider the compound water made up of two atoms of hydrogen

(H) for every atoms of oxygen (O) Can be presented chemical formula H20

Sample A and Its Composition Sample A and Its Composition

10.000 g 27.000 g

1.119 g H % H=11.19 3.021 g H % H=11.19

8.881 g O % O= 88.81 23.979 g O % O= 88.81

Two samples describes below have the same proportions of the two

elements

Exp: determine the percent by mass of hydrogen Simple divide the mass of hydrogen by the sample mass and multiply

by 100%. For each sample, you will obtain the same results:11.19%

H

Dalton’s Atomic Theory: John Dalton

Describes the basis of atomic theory with three assumptions

1. Each element is composed of small particles called atoms. Atoms

are neither created nor destroyed in chemical reactions.

2. All atoms of a given element are identical but atoms of one

element are different from those off all other elements

3. Compounds are formed when atoms of more than one element

combine in simple numerical ratios.

exp: one atom of A to two B (AB2)

Molecules of CO and CO2Figure 2-3

In forming carbon monoxide (CO), 1.0 g of carbon combines with 1.33 g of oxygen.

In forming carbon dioxide (CO2), 1.0 g of carbon combines with 2.66 g of oxygen.

The second oxide is richer in O

It contains twice as much O as the first

2-2 Electrons and Other Discoveries in Atomic Physics

Electricity and magnetism were used in the experiment so that led to the current

theory of atomic structure

Certain objects displays a properties called electric charge, which can be either

positive (+) or negative (-)

An object having equal number of (+) or (-) charged particles carries no net

charge and is electrically neutral

If the number of (+) charge exceed the number of (-) charge , the object has a net

positive charge

If the number of (-) charge exceed the number of (+) charge , the object has a net

negative charge

(+) and (-) charges attract each other , while two (+) and two (-) charges repel

each other

(a) Electrostatically charged comb. If you comb your hair the static charge

develop on the comb and causes bits of paper to be attracted to the comb

(b) Both objects on the left carry negative charge repel each other

The objects in the center lack any electrical charge and exert no force on each other

The object on the right carry opposite charges and attract each other

Forces between electrically charged objectsFIGURE 2-4

Cathode ray tubeFIGURE 2-6

The Discovery of Electrons Faraday discovered cathode rays, a type of radiation emitted by a (-) terminal, or

cathode (it is iron, platinum so on) The radiation crossed the evacuated tube to the (+) terminal, or anode

The high voltage source of electricity creates a (-) charge on the electrode at the left

(cathode) and a (+) charge on the electrode at the right (anode)Cathode rays pass from the cathode (C) to the anode (A) which is perforated to

allow the passage of a narrow beam of the cathode rays They are visible only through the green florescence that they produce on the zinc

sulfide-coated screen at the end of the tube. They are in the other part s of the tube

Cathode rays and their propertiesFIGURE 2-7

C rays are deflected by electric and magnetic fields in the manner expected for

negatively charged particles (Figure 2-7 (a) and (b))

Figure 2-7 (c) determine the mass to charge ratio m/e for the C rays

Cathode rays subsequently become known as electrons

Electron m/e = -5.6857 × 10-9 g coulomb-1

Millikan’s oil-drop experimentFigure 2-8

Robert Millikan determined the electronic charge , e through a serious oil drop experiment

He showed ionized oil drops can be balanced against the pull of gravity by an electric field

e is -1.6022x10-19 coulomb

mass of electron= (-1.6022x10-19 coulomb) x (-5.6857 × 10-9 g coulomb-1 ) = 9.1094 x 10-28 g

Plum-pudding Model Proposed by Thomson

Explains how the electron particles were incorporated

into atoms.

He thought that the positive charge necessary to

counter balance the negative charges of electrons in a

neutral atom was the form of a nebulous cloud.

He suggest, electrons floated in a diffuse cloud of

positive charge

A helium atom would have a +2 cloud of (+) charge and

two electrons (-2)

If helium atom loses one electron, it becomes charged

and is called an ion referred to He+ has a net charge of 1+

If the helium atom loses both electron the He2+ ion forms

X-Rays and Radioactivity

X-ray is form of high energy electromagnetic radiation

Radioactivity is the spontaneous emission of radiation

from a substance

Two types of radiation form from radioactive material

were identified by Ernest Rutherford

Alpha ( ): a a-particles carry two fundamental units of

positive charge and the same mass as helium atoms.

This particle are identical to He2+ions

Beta ( ): b b-particles are negatively charged and have

the same properties as electrons

Gamma ( ) g rays: is not effected by electric or magnetic

field. It is not made of particles. It is electromagnetic

radiation of extremely high penetrating power.

The scattering of a- particles by metal foil

Figure 2-11

2-3 The Nuclear Atom Rutherford used the a-particles to study inner structure of the atoms The telescope travels in a circular track around at evacuated chamber containing

the metal foil. Most a-particles pass thought the metal foil undeflected , but some are deflected

through large angles

The nuclear atom have these features below Most of mass and all of positive charge of an atom are centered in a very

small region called nucleus. The remainder of the atom is mostly empty space The magnitude of the positive charge is different for the different atoms and

is approximately one-half the atomic weight of the elementThere are as many electrons outside the nucleus as there are unit of positive

charge on the nucleus. The atom as a whole is electrically neutral.

The nuclear atom – illustrated by the helium atom

Figure 2-13

Properties of Protons, neutrons and Electrons

Protons: positively charged

fundamental particles of the matter in

the nuclei of atoms

Neutrons: penetrating radiation

consisted of beam of neutral particles

The number of protons in a given atom

is called the atomic number, or the

proton number, Z

The number of electrons in the atom is

equal to Z because the atom is

electrically neutral

The total number of proton and

neutrons in an atom is called the mass

number, A

The number of neutron is A-Z and

electrically neutral.

2-4 Chemical Elements

To represent a particular atom we use symbolism

A= mass number Z = atomic number

Each element has a name and distinctive symbol

Exp: carbon:C, oxygen:O, neon:Ne, iron:Fe

Symbol of element

Al13

27

Has 13 protons and 14 neutrons in its nucleus

and 13 electron outside the nucleus (recall that

an atom has the same number of electrons as

protons)

Isotopes

atoms that have the same atomic number (Z) but different masss number (A) are

called isotopes.

Ne10

20

Exp: all neon atoms have 10 protons in their nuclei, and most have 10 neutron as well. A very few neon atoms have 11 neutrons and some have 12

Ne10

21 Ne10

22

Ions When atoms lose or gain electrons the species formed are called ions and

carry net charges. Removing electrons result in positively charged ion The number of proton does not change when an atom becomes an ion. Exp:

Ne10

22 2+

Ne10

20 +

O8

16 2-

10 protons 10 neutrons and 9 electrons

10 protons 12 neutrons and 8 electrons

8 protons 8 neutrons and 10 electrons

A mass spectrometer and a mass spectrumFigure 2-14

Isotopic masses

Used when original mass of an atoms can not be determined That must be done by experiment One type of atom has been chosen and assigned a specific mass. This standard

is an atom of the isotope carbon-12 Next the masses of the other atoms relative to carbon -12 are determined with

a mass spectrometer

2-5 Atomic Mass

Weighted AverageAtomic Mass of an Element

fractional abundance of isotope 1

atomic mass of isotope 1

fractional abundance of isotope 2

atomic mass of isotope 2

= x x+

Aave x1 A1= x x2 x A2+ + …… xn x An

+ ……

where x1 + x2+ …..+ xn = 1.0

Equation (2.3)

The average of the isotopic masses, weighted according to the naturally occurring abundance of the isotopes of the elements

2-6 Introduction to The Periodic Table

The classification system we need known as the periodic table of the elements

We will discuss these in detail in Chapter 9.

Read atomic massesRead the ions formed by main group elementsRead the electron configurationLearn trends in physical and chemical properties

The Periodic tableAlkali Metals

Alkaline Earths

Transition Metals

Halogens

Noble Gases

Lanthanides and Actinides

Main Group

Main Group

2-7 The Concept of the Mole and the Avogadro Constant

Exp:

1 mol 12C = 6.02214179 x 1023 12C atoms = 12 g

1 mol 16O = 6.02214179 x 1023 16O atoms = 15.9949 g (and so on)

A mole: is the amount of the substance that contains the same number of

elementary entities (atoms, molecules and so on)

Avogadro constant or Avogadro number, NA: The amount of elementary

entities in a mole

NA = 6.02214179 x 1023 mol-1

Molar mass, M: the mass of one mole of substance , from a table of atomic masses

Exp: the molar mass of lithium is 6.941 g/mol Li