01- Ch02 Atoms and the Atomic Theory

8/7/2019 01- Ch02 Atoms and the Atomic Theory

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Cha ter 2: Atoms and the Atomic Theor

General ChemistryPrinciples and Modern Applications

Petrucci Harwood Herring

8th Edition

Prentice-Hall 2002General Chemistry: Chapter 2Slide 1 of 25

Philip Dutton

University of Windsor, Canada

Prentice-Hall 2002


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Contents

Early chemical discoveries

Electrons and the Nuclear Atom

Chemical Elements


Atomic Masses The Mole


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Early Discoveries

Lavoisier 1774 Law of conservation of mass

Proust 1799 Law of constant composition


Dalton 1803-1888 Atomic Theory


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Daltons Atomic Theory

Each element is composed of small particles called atoms.

Atoms are neither created nor destroyed in chemical reactions.


Compounds are formed when atoms of more than one element

combine


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Consequences of Daltons theory

In forming carbon monoxide, 1.33 gof oxygen combines with 1.0 g of

Law of Definite Proportions: combinations of elements arein ratios of small whole numbers.


car on.

In the formation of carbon dioxide2.66 g of oxygen combines with 1.0 g

of carbon.


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Behavior of charges



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Cathode ray tube



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Properties of cathode rays


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


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Charge on the electron


From 1906-1914 Robert Millikan showed ionized oil dropscan be balanced against the pull of gravity by an electric field.The charge is an integralmultiple of the electronic charge, e.


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Radioactivity

Radioactivity is the spontaneous emission of radiationfrom a substance.

X-rays and -rays are high-energy light.


-par c es are a s ream o e um nuc e , e+

. -particles are a stream of high speed electrons

that originate in the nucleus.


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The nuclear atom

Geiger and Rutherford1909



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The -particle experiment

Most of the mass and all of thepositive charge is concentrated in asmall region called the nucleus .


There are as many electrons outsidethe nucleus as there are units ofpositive charge on the nucleus


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The nuclear atom

Rutherfordprotons 1919


James Chadwickneutrons 1932


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Atomic Diameter 10-8 cm Nuclear diameter 10-13 cm

Nuclear Structure

Particle Mass Charge

1


kg amu Coulombs (e)Electron 9.109 x 10-31 0.000548 1.602 x 10-19 1Proton 1.673 x 10-27 1.00073 +1.602 x 10-19 +1

Neutron 1.675 x 10-27 1.00087 0 0


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Scale of Atoms

Useful units:

1 amu (atomic mass unit) = 1.66054 x 10-24 kg

The heaviest atom has a mass of only 4.8 x 10-22 gand a diameter of only 5 x 10-10 m.


1 pm (picometer) = 1 x 10-12 m 1 (Angstrom) = 1 x 10-10 m = 100 pm = 1 x 10-8 cm

Biggest atom is 240 amu and is 50 across.Typical C-C bond length 154 pm (1.54 )

Molecular models are 1 /inch or about 0.4 /cm


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Isotopes, atomic numbers and mass numbers

To represent a particular atom we use the symbolism:


A= mass number Z = atomic number


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Measuring atomic masses



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The Periodic tableAlkali Metals

Alkaline Earths

Transition Metals

Halogens

Noble Gases

Main Group


Lanthanides and ActinidesMain Group


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The Periodic Table

Read atomic masses.

Read the ions formed by main group elements.

Read the electron configuration.


Learn trends in physical and chemical properties.

We will discuss these in detail in Chapter 10.


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The Mole

Physically counting atoms is impossible.

We must be able to relate measured mass to

numbers of atoms.


buying nails by the pound. using atoms by the gram


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Avogadros number

The mole is an amount of substance that

contains the same number of elementaryentities as there are carbon-12 atoms in

exactl 12 of carbon-12.


NA = 6.02214199 x 1023 mol-1


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Molar Mass

The molar mass, M, is the mass of one mole

of a substance.


M(g/mol 12C) = A(g/atom 12C) x NA (atoms 12C /mol 12C)


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Combining Several Factors in a CalculationMolar Mass, the

Avogadro Constant, Percent Abundance.

Potassium-40 is one of the few naturally occurring radioactiveisotopes of elements of low atomic number. Its percent natural

abundance among K isotopes is 0.012%. How many 40K

Example 2-9


containing 371 mg of K?

Want atoms of40K, need atoms of K,

Want atoms of K, need moles of K,Want moles of K, need mass and M(K).


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Convert strategy to plan

mK(mg) x (1g/1000mg) mK (g) x 1/MK (mol/g) nK(mol)

Convert mass of K(mg K) into moles of K (mol K)

nK = (371 mg K) x (10-3 g/mg) x (1 mol K) / (39.10 g K)

and plan into action


Convert moles of K into atoms of40K

nK(mol) x NA atoms K x 0.012% atoms40K

= . x - mo

atoms 40K = (9.49 x 10-3 mol K) x (6.022 x 1023 atoms K/mol K)

x (1.2 x 10-4 40K/K)

= 6.9 x 1017 40K atoms

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01- Ch02 Atoms and the Atomic Theory