The Nuclear Atom• Rutherford modified Thomson’s

model:– assume the atom is spherical

but the positive charge must be located at the center (it’s small and dense), with a diffuse negative charge surrounding it

– Read section 2.2 for all of the details on the experiments!

Text, P. 40

21

2.3 The Modern View of Atomic Structure

The atom consists of positive, negative, and neutral entities (protons, electrons, and neutrons)

• Nucleus:• Small• Dense (Protons and neutrons)• Massive (Protons and neutrons)

• Isotopes have the same number of protons but different numbers of neutrons

• Electrons are located outside of the nucleus • Most of the volume is due to the electron cloud

31Text, P. 42

41

Isotopes, Atomic Numbers, and Mass Numbers

• Atomic number (Z) = number of protons in the nucleus

• Mass number (A) = total number of protons and neutrons in the nucleus

• For element X, we write X• Isotopes have the same Z but different A

Z

A

51

Atomic Number

Average Atomic Mass

(Mass Number = 24)

61

Sample Problems: # 15 & 19

71

2.4 Atomic Weights

The Atomic Mass Scale• 1 atom of 1H weighs 1.6735 x 10-24 g and 1 atom of 16O weighs

2.6560 x 10-23 g

• We define: mass of 12C = exactly 12 amu• Using atomic mass units:

1 amu = 1.66054 x 10-24 g1 g = 6.02214 x 1023 amu

81

• Sample Problem: # 73 a and 75

91

Average Atomic Masses

• Relative atomic mass: average masses of isotopes:– Naturally occurring C: 98.892 % 12C + 1.108 % 13C

• Average mass of C: • (0.98892)(12 amu) + (0.0108)(13.00335) = 12.011 amu

• Atomic weight (AW) is also known as average atomic mass

101

Sample Problem: # 23

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2.5 The Periodic Table

• The Periodic Table is used to organize the elements in a meaningful way• Dimitri Mendeleev: Periodic properties• IUPAC: governing body of chemistry

The Periodic Table

92 naturally occurring elements

Others are synthetic

Metalloids have the appearance of metals and the behavior of nonmetals

131

Metals, Nonmetals, and Metalloids

Increasing Metallic Character

141

GroupsAlkali metals

(no H)Alkaline Earth

metals

HalogensNoble Gases

Transition metals

No Group #s

Innertransition metals

Chalcogens

Lanthanides

Actinides

151

PeriodsPerio

d

#

2

1

3

5

4

7

6

161

2.6 Molecules and Molecular Compounds

Molecules and Chemical Formulas• Molecules: two or more atoms bonded together

• The chemical formula indicates the type and number of atoms in the molecule• Compounds formed from molecules are molecular

compounds• Molecules that contain two atoms bonded together

are called diatomic molecules• 2 of the same element

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The Diatomic Molecules

Text, P. 50

“Oh I have nice closets for brooms!” ~ Mat Golden, 10/3/06

181

Molecular and Empirical Formulas

• Molecular formulas– give the actual numbers and types of atoms in a

molecule– Examples: H2O, CO2, CO, CH4, H2O2, O2, O3, and C2H4

191

• Empirical formulas

– give the lowest whole number ratio of atoms in a molecule

– Examples: H2O, CO2, CO, CH4, HO, CH2

201

Picturing Molecules

Text, P. 51

(nothing to copy from this slide)

211

• Sample problems # 37, 41