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1
Chapter 3
Atomic Structure and the Periodic Table
2
Atomic Theory

• 420 B.C. Democritus developed the idea that the
  atom is indestructible and indivisible
• 2200 years later Dalton reinforced idea w/ his
  atomic theory using a model

3
What is a model??

• Representation of what scientist believe the atom
  is like
• Based on
• Observations
• Experimental Results
• Reasoning

4
Daltons Atomic Theory

• All matter is composed of very tiny particles,
  which Dalton called atoms
• All atoms of the same element have the same
  chemical properties
• Compounds are formed by the chemical combination
  of two or more of the same or different kinds of
  atoms
• A molecule is a tightly bound combination of two
  or more atoms that acts as a unit

5
Atomic Theory

• Atoms are building blocks of elements
• Similar atoms in each element
• Different from atoms of other elements
• Two or more different atoms bond in simple ratios
  to form compounds

6
Daltons Theory???

• Laid foundation for current atomic theory
• Indivisibility later shown to be incorrect
• Not all atoms have same, size, mass, and form

7
Subatomic Particles
Particle Symbol Charge Relative Mass
Electron e- 1- 0 Proton p
1 Neutron n 0 1
8
Location of Subatomic Particles

• 10-13 cm
• electrons
• protons
• neutrons
• 10-8 cm

nucleus
9
Atomic Number
Counts the number of protons in an atom
10
Atomic Number on the Periodic Table
11 Na
Atomic Number
Symbol
11
All atoms of an element have the same number of
protons
11 Na
11 protons
Sodium
12
Learning Check
State the number of protons for atoms of each
of the following A. Nitrogen 1) 5 protons
2) 7 protons 3) 14 protons B. Sulfur
1) 32 protons 2) 16 protons 3) 6
protons C. Barium 1) 137 protons 2) 81
protons 3) 56 protons
13
Solution
State the number of protons for atoms of each
of the following A. Nitrogen 2) 7
protons B. Sulfur 2) 16 protons C.
Barium 3) 56 protons
14
Mass Number
Counts the number of protons and neutrons in
an atom
15
Atomic Mass on the Periodic Table
11 Na 22.99
Atomic Number
Symbol
Atomic Mass
16
Number of Electrons

• An atom is neutral
• The net charge is zero
• Number of protons Number of electrons
• Atomic number Number of electrons

17
Subatomic Particles in Some Atoms
16 31 65 O P Zn
8 15 30 8 p 15 p 30 p 8 n 16 n 35
n 8 e- 15 e- 30 e-
18
Learning Check
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom 1)
30 2) 35 3) 65 B. Number of neutrons in
the zinc atom 1) 30 2) 35 3) 65 C.
What is the mass number of a zinc isotope
with 37 neutrons? 1) 37 2) 65 3) 67
19
Solution
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom 1)
30 B. Number of neutrons in the zinc
atom 2) 35 C. What is the mass number of
a zinc isotope with 37 neutrons? 3) 67
20
Learning Check
Write the atomic symbols for atoms with the
following A. 8 p, 8 n, 8 e- ___________ B.
17p, 20n, 17e- ___________ C. 47p, 60 n,
47 e- ___________
21
Solution
16O A. 8 p, 8 n, 8 e- 8 B. 17p,
20n, 17e- 37Cl 17 C. 47p, 60 n, 47
e- 107Ag 47
22
Learning Check AT 5
An atom has 14 protons and 20 neutrons. A. Its
atomic number is 1) 14 2) 16 3) 34 B.
Its mass number is 1) 14 2) 16 3) 34 C.
The element is 1) Si 2) Ca 3)
Se D. Another isotope of this element is 1)
34X 2) 34X 3) 36X 16
14 14
23
Solution AT 5
An atom has 14 protons and 20 neutrons. A. It
has atomic number 1) 14 B. It has a mass
number of 3) 34 C. The element is 1)
Si D. Another isotope of this element would
be 3) 36X 14
24
Atomic Mass
Atomic mass is the weighted average mass of all
the atomic masses of the isotopes of that atom.
25
Atomic Mass
Na 22.99

• Listed on the periodic table
• Gives the mass of average atom of each element
  compared to 12C
• Average atom based on all the isotopes and their
  abundance
• Atomic mass is not a whole number

26
Isotopes

• Atoms with the same number of protons, but
  different numbers of neutrons.
• Atoms of the same element (same atomic number)
  with different mass numbers
• Isotopes of chlorine
• 35Cl 37Cl
• 17 17
• chlorine - 35 chlorine - 37

27
Learning Check
Naturally occurring carbon consists of three
isotopes, 12C, 13C, and 14C. State the number of
protons, neutrons, and electrons in each of these
carbon atoms. 12C 13C 14C
6 6 6 p
_______ _______
_______ n _______ _______
_______ e _______
_______ _______
28
Solution
12C 13C 14C 6
6 6 p 6
6 6 n 6
7 8 e 6 6
6
29
Calculating Atomic Mass

• Percent() abundance of isotopes
• Mass of each isotope of that element
• Weighted average
• mass isotope1() mass isotope2()
• 100 100

30
Example of an Average Atomic Mass
Cl-35 is about 75.5 and Cl-37 about 24.5 of
natural chlorine. 35 x 75.5 26.4
100 35.5 37 x
24.5 9.07 100
31
Atomic Mass of Magnesium
Isotopes Mass of Isotope Abundance
24Mg 24.0 amu 78.70 25Mg
25.0 amu 10.13 26Mg
26.0 amu 11.17
32
Learning Check AT7

• Gallium is a metallic element found in small
  lasers used in compact disc players. In a sample
  of gallium, there is 60.2 of gallium-69 (68.9
  amu) atoms and 39.8 of gallium-71 (70.9 amu)
  atoms. What is the atomic mass of gallium?

33
Solution AT7
Ga-69 68.9 amu x 60.2 41.5 amu for
69Ga 100 Ga-71
(/100) 70.9 amu x 39.8 28.2 amu for
71Ga 100 Atomic mass
Ga 69.7 amu
34
Elements

• Pure substances that cannot be separated into
  different substances by ordinary processes
• Are the building blocks of matter
• 112 elements known today
• Examples carbon
• gold
• calcium

35
Periodic Table

• A systematic catalog of elements.
• Elements are arranged in order of atomic number.

36
Periodicity

• When one looks at the chemical properties of
  elements, one notices a repeating pattern of
  reactivities.

37
Periodic Table

• The rows on the periodic chart are periods.
• Columns are groups.
• Elements in the same group have similar chemical
  properties.

38
Groups

• These five groups are known by their names.

39
Periodic Table

• Nonmetals are on the right side of the periodic
  table (with the exception of H).

40
Periodic Table

• Metalloids border the stair-step line (with the
  exception of Al and Po).

41
Periodic Table

• Metals are on the left side of the chart.

42
Metals and Nonmetals

• Metals
• Located to the left of the heavy line
• Shiny, ductile
• Good conductors of heat and electricity
• Nonmetals
• Located to the right of the heavy line
• Dull and brittle
• Poor conductors, good insulators

43
Learning Check
A. Element in Group VIIA, period 4 1) Br 2)
Cl 3) Mn B. Element in Group IIA, Period 3
1) beryllium 2) magnesium 3) boron C. Metals
in Group IVA 1) Ge, Sn, Pb 2) C, Si
3) C, Si, Ge, Sn D. Nonmetals in Group VA 1)
As, Sb, Bi 2) N, P, As 3) N, P, As, Sb
44
Solution
A. Element in Group VIIA, period 4 1) Br B.
Element in Group IIA, Period 3 2) magnesium C.
Metals in Group IVA 1) Ge, Sn, Pb D.
Nonmetals in Group VA 2) N, P, As
45
Learning Check
Specify metal (1) or nonmetal (2) for each A.
sulfur ____ B. chlorine ____ C. sodium ____ D.
iron ____ E. carbon ____ F. silver ____
46
Solution
Specify metal (1) or nonmetal (2) for each A.
sulfur 2 B. chlorine 2 C. sodium 1 D.
iron 1 E. carbon 2 F. silver 1
47
Learning Check
Select the correct elements A. Metals in Group
IVA 1) Ge, Sn, Pb 2) C, Si 3)
C, Si, Ge, Sn B. Nonmetals in Group VA 1)
As, Sb, Bi 2) N, P, As 3) N, P,
As, Sb
48
Solution
A. Metals in Group 4A 1) Ge, Sn, Pb
B. Nonmetals in Group 5A 2) N, P, As
49
Characteristics of Electrons

• Extremely small mass
• Located outside the nucleus
• Moving at extremely high speeds in a sphere
• Have specific energy levels

50
Energy of Electrons

• When atoms are heated, bright lines appear called
  line spectra
• Electrons in atoms arranged in discrete levels.
• An electron absorbs energy to jump to a higher
  energy level.
• When an electron falls to a lower energy level,
  energy is emitted.

51
Bohr Model

• First model of the electron structure
• Gives levels where an electron is most likely to
  be found
• Incorrect today, but a key in understanding the
  atom

52
Quantum Mechanics
Describes the arrangement and space occupied by
electrons in atoms
53
Electron Levels (Shells)

• Contain electrons that are similar in energy and
  distance from nucleus
• Low energy electrons are closest to the nucleus
• Identify by numbers 1, 2, 3, 4, 5, 6..
• The first shell (1) is lowest in energy, 2nd
  level next and so on 1lt2lt3lt4

54
Number of Electrons

• Maximum number of electrons in any electron
  level 2n2
• n 1 2(1)2 2
• n 2 2(2)2 8
• n 3 2(3)2 18

55
Order of Electron Filling

• All electrons in the same energy level have
  similar energy.
• Shell 1 2 electrons
• Shell 2 8 electrons
• Shell 3 18 electrons (8 first, later 10)
• Order of filling for the first 20 electrons
• Shell 1 2 3 4
• 2e 8e 8e 2e

56
Electron Configuration

• Lists the shells containing electrons
• Written in order of increasing energy
• Element Shell 1 2 3
• He 2
• C 2 4
• F 2 7
• Ne 2 8
• Al 2 8 3
• Cl 2 8 7

57
Learning Check EA2
A. The electron configuration for sulfur 1)
2,6 2) 8,2,6 3) 2, 8, 6 B. The element in period
3 with two electrons in the outermost energy
level 1) Mg 2) Ca 3) Be
58
Subshells and Orbitals

59
Quantum Mechanics

• Describes the arrangement of electrons in atoms
  in terms of
• Main or principal energy levels (n)
• Energy subshells
• Orbitals (space occupied within the atom)

60
Principal Energy Levels (n)

• Contain electrons that are
• Close in energy
• Similar distance from nucleus
• Have values of n 1, 2, 3, 4, 5, 6..
• Maximum number of electrons 2n2
• n 1 2(1)2 2
• n 2 2(2)2 8
• n3

61
Energy Levels (Shells)

• A group of electrons in an atom all having the
  same principal quantum number (n)
• n 1, 2, 3,
• The first shell (n 1) is lowest in energy, 2nd
  level next and so on 1lt2lt3lt4
• The number of electron in each shell is limited
  to 2n2
• n 1 2n2 2
• n 2 2n2 ____

62
Subshells

• Energy sublevels within energy level
• All electrons in a subshell have the same energy
• Designated s, p, d, f ..
• Sublevel energy sltpltdltf

63
Electron Locations
Main Energy Levels Sublevels n4 4s,
4p, 4d, 4f n3 3s, 3p, 3d n2 2s, 2p n1 1s
64
Electrons Allowed

• All electrons in the same sublevel have the same
  energy.
• All 2s electrons have the same energy. All 2p
  electrons have the same energy which is slightly
  higher than the energy of the 2s electrons
• s sublevel 2 electrons
• p sublevel 6 electrons
• d sublevel 10 electrons
• f sublevel 14 electrons

65
Order of Filling
66
Electron Configurations

• Distribution of all electrons in an atom
• Consist of
• Number denoting the energy level

67
Electron Configurations

• Distribution of all electrons in an atom
• Consist of
• Number denoting the energy level
• Letter denoting the subshell

68
Electron Configurations

• Distribution of all electrons in an atom.
• Consist of
• Number denoting the energy level.
• Letter denoting the type of orbital.
• Superscript denoting the number of electrons in
  those orbitals.

69
Electron Configuration

• List of subshells containing electrons
• Written in order of increasing energy
• Superscripts give the number of electrons
• Example Electron configuration of neon
• number of electrons
• 1s2 2s2 2p6
• main shell subshell

70
Writing Electron Configurations
H 1s1 He 1s2 Li
1s2 2s1 C 1s2 2s2 2p2 S 1s2 2s2 2p6 3s2 3p4
71
Learning Check S3
Using the periodic table, write the complete
electronic configuration for each A. Cl B.
Sr C. I
72
Solution S3
Using the periodic table, write the complete
electronic configuration for each A. Cl 1s2
2s2 2p6 3s2 3p5 B. Sr 1s2 2s2 2p6 3s2 3p6
4s2 3d10 4p6 5s2 C. I 1s2 2s2 2p6 3s2 3p6 4s2
3d10 4p6 5s2 4d10 5p5
73
Periodic Table

• We fill orbitals in increasing order of energy.
• Different blocks on the periodic table, then
  correspond to different types of orbitals.

74
Orbital

• A 3 dimensional space around a nucleus in which
  electrons are most likely to be found
• Shape represents electron density (not a path the
  electron follows)
• Each orbital can hold up to 2 electrons.

75
s Orbitals

• Spherical in shape.
• Radius of sphere increases with increasing value
  of n.

76
p Orbitals

• Have two lobes with a node between them.

77
d Orbitals

• Four of the five
• orbitals have 4
• lobes the other
• resembles a p
• orbital with a
• doughnut around
• the center.

78
Learning Check S5
A. Number of electrons in a p orbital 1) 1e 2)
1e or 2e 3) 3e B. Number of orbitals in a p
subshell 1) 1 2) 2 3) 3 C. Number of
orbitals in 4d subshell 1) 1 2) 3 3) 5 D.
Number of electrons (maximum) in a 3d
subshell 1) 2e 2) 5e 3) 10e
79
Solution S5
A. Number of electrons in a p orbital 2) 1e or
2e B. Number of orbitals in a p subshell 3)
3 C. Number of orbitals in 4d subshell 3) 5 D.
Number of electrons in a 3d subshell 3) 10e
80
Orbital Diagrams

• Use individual orbitals
• Give subshell arrangement
• Each orbital takes one electron before any other
  orbital in the same subshell can receive a second
  electron

81
Orbital Diagrams

• Each box represents one orbital.
• Half-arrows represent the electrons.
• The direction of the arrow represents the spin of
  the electron.

82
Hunds Rule

• For degenerate orbitals, the lowest energy is
  attained when the number of electrons with the
  same spin is maximized.

83
SAMPLE INTEGRATIVE EXERCISE Putting Concepts
Together
Boron, atomic number 5, occurs naturally as two
isotopes, 10B and 11B, with natural abundances of
19.9 and 80.1, respectively. (a) In what ways
do the two isotopes differ from each other? Does
the electronic configuration of 10B differ from
that of 11B? (b) Draw the orbital diagram for an
atom of 11B. Which electrons are the valence
electrons? (
The valence electrons are the ones in the
outermost occupied shell, the 2s2 and 2p1
electrons. The 1s2 electrons constitute the core
electrons, which we represent as He when we
write the condensed electron configuration,
He2s22p1.

84
Orbital Diagram for nitrogen
N 1s 2s 2p
??
??
?
?
?
85
Orbital Diagram for A Fluorine Atom
F 1s 2s 2p
3s
??
??
?
??
??
86
Orbital Diagram for A Magnesium Atom
Mg 1s 2s 2p
3s
??
??
??
??
??
??
87
Learning Check O1
Write the orbital diagram for the electrons in
an oxygen atom.
88
Solution O1
Write the orbital diagram for the electrons in
an oxygen atom. 1s 2s
2p
??
??
?
??
?
89
Learning Check O2
Write the orbital diagram for the electrons in
an iron atom.
90
Solution O2
Write the orbital diagram for the electrons in
an iron atom. 1s 2s 2p
3s 3p 3d
??
??
??
??
??
??
??
??
??
?
?
?
?
??