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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
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Atomic Masses The Mole
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Early Discoveries
Lavoisier 1774 Law of conservation of mass
Proust 1799 Law of constant composition
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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.
Prentice-Hall 2002General Chemistry: Chapter 2Slide 4 of 25
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.
Prentice-Hall 2002General Chemistry: Chapter 2Slide 5 of 25
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
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Electron m/e = -5.6857 x 10-9 g coulomb-1
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Charge on the electron
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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.
Prentice-Hall 2002General Chemistry: Chapter 2Slide 10 of 25
-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 .
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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
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James Chadwickneutrons 1932
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Atomic Diameter 10-8 cm Nuclear diameter 10-13 cm
Nuclear Structure
Particle Mass Charge
1
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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.
Prentice-Hall 2002General Chemistry: Chapter 2Slide 15 of 25
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:
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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
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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.
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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.
Prentice-Hall 2002General Chemistry: Chapter 2Slide 20 of 25
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.
Prentice-Hall 2002General Chemistry: Chapter 2Slide 21 of 25
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.
Prentice-Hall 2002General Chemistry: Chapter 2Slide 22 of 25
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
Prentice-Hall 2002General Chemistry: Chapter 2Slide 23 of 25
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
Prentice-Hall 2002General Chemistry: Chapter 2Slide 24 of 25
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