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Chapter 3
Atoms and Elements
1
3.1
Elements and Symbols
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Elements
2
Elements are
• pure substances that cannot be separated into simpler
substances by ordinary laboratory processes
• the building blocks of matter
• listed on the inside front cover of this text
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Some Elements and Their Names
3
Names come from:
• planets
• mythological figures
• minerals
• colors
• geographic locations
• famous people
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Chemical Symbols
4
Chemical Symbols
• represent name of element
• consist of one to two letters and start with capital
1-Letter Symbols 2-Letter Symbols
C carbon
Co cobalt
N nitrogen
Ca calcium
F fluorine
Al aluminum
O oxygen
Mg magnesium
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Chemical Symbols from Latin Names
5
Ag
silver, from argentum
Au
gold, from aurum
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Learning Check
6
Write the correct chemical symbols for each of the
following elements:
A. iodine
B. iron
C. magnesium
D. zinc
E. nitrogen
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Solution
7
Write the symbols for each of the following elements:
A. iodine
= I
B. iron
= Fe
C. magnesium
= Mg
D. zinc
= Zn
E. nitrogen
=N
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Learning Check
8
Give the names of the elements with the following symbols:
A. P
B. Al
C. Mn
D. H
E. K
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Solution
9
Give the names of the elements with the following symbols:
A. P
= phosphorus
B. Al
= aluminum
C. Mn
= manganese
D. H
= hydrogen
E. K
= potassium
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Chapter 3
Atoms and Elements
10
3.2
The Periodic Table
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Groups and Periods
11
On the periodic table,
• elements are arranged according to similar properties
• groups contain elements with similar properties in
vertical columns
• periods are horizontal rows of elements
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Groups and Periods
12
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Periodic Table of Elements
13
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Group Numbers
14
Group numbers
• use the letter A for representative elements
(Groups 1A–8A)
• use the letter B for transition elements
(Groups 3B–12B)
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Classification of Groups
15
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Alkali Metals
16
Group 1A, the alkali metals,
includes lithium, sodium,
potassium, rubidium, and
cesium.
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Halogens
17
Group 7A, the halogens,
includes chlorine, bromine,
and iodine.
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Learning Check
18
Identify the element described by the following:
1. Group 7A, Period 4
A. Br
B. Cl
C. Mn
2. Group 2A, Period 3
A. beryllium
B. boron
C. magnesium
3. Group 5A, Period 2
A. phosphorus
B. arsenic
C. nitrogen
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Solution
19
Identify the element described by the following:
1. Group 7A, Period 4
A. Br
2. Group 2A, Period 3
C. magnesium
3. Group 5A, Period 2
C. nitrogen
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Metals, Nonmetals, and Metalloids
20
The heavy zigzag line separates metals and nonmetals.
• Metals are located to the left.
• Nonmetals are located to the right.
• Metalloids are located along the heavy zigzag line
between the metals and nonmetals.
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Metals, Nonmetals, and Metalloids and
Periodic Table
21
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Properties of Metals, Nonmetals, and
Metalloids
22
Metals
• are shiny and ductile
• are good conductors of heat and electricity
Nonmetals
• are dull, brittle, and poor conductors
• are good insulators
Metalloids
• are better conductors than nonmetals, but not as good
as metals
• are used as semiconductors and insulators
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Comparing a Metal, Nonmetal, and
Metalloid
23
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Learning Check
24
Identify each of the following elements as a metal, nonmetal, or
metalloid.
A. sodium
B. chlorine
C. silicon
D. iron
E. carbon
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Solution
25
Identify each of the following elements as metal, nonmetal, or
metalloid.
A. sodium
metal
B. chlorine
nonmetal
C. silicon
metalloid
D. iron
metal
E. carbon
nonmetal
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Learning Check
26
List all of the elements that match the description
A. Metals in Group 4A
Sn, Pb, C, Si, Ge
B. Nonmetals in Group 5A
As, Sb, Bi, N, P, As, Sb
C. Metalloids in Group 4A
C, Si, Ge, Sn, Pb
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Solution
27
List all of the elements that match the description
A. Metals in Group 4A
Sn, Pb
B. Nonmetals in Group 5A
N, P
C. Metalloids in Group 4A
Si, Ge
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Chapter 3
Atoms and Elements
28
3.3
The Atom
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Dalton's Atomic Theory
29
In Dalton's atomic theory, atoms
• are tiny particles of matter
• of an element are similar to each other and different
•
•
from other elements
of two or more different elements combine to form
compounds
are rearranged to form new combinations in a chemical
reaction
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Subatomic Particles Electrical Charges
30
Atoms contain subatomic
particles.
• Protons have a positive (+)
charge.
• Electrons have a negative (–
) charge.
• Neutrons are neutral.
• Like charges repel and unlike
charges attract.
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Rutherford's Gold Foil Experiment
31
In Rutherford’s gold foil experiment, positively
charged particles
•
were aimed at atoms of gold
•
mostly went straight through the atoms
•
were deflected only occasionally
Conclusion:
There must be a small, dense, positively charged
nucleus in the atom that deflects positive particles that
come close.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Rutherford's Gold Foil Experiment
32
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Structure of the Atom
33
An atom consists of
• a nucleus that
contains protons
and neutrons
• electrons in a large,
empty space around
the nucleus
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Mass of the Atom
34
Atomic mass unit
• 1 atomic mass unit (amu) has a mass equal to 1/12 of the
mass of the carbon-12 atom.
• a proton has a mass of about 1 (1.007) amu.
• a neutron has a mass of about 1 (1.008) amu.
• an electron has a very small mass, 0.000 549 amu.
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Subatomic Particles in the Atom
35
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Learning Check
36
Which of the following subatomic particles fits each of the
descriptions below:
proton, neutrons, or electrons
A. found outside the nucleus
B. has a positive charge
C. has mass but no charge
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Solution
37
Which of the following subatomic particles fits each of the
descriptions below:
proton, neutrons, or electrons
A. found outside the nucleus
B. has a positive charge
C. has mass but no charge
electrons
protons
neutrons
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Chapter 3
Atoms and Elements
38
3.4
Atomic Number and Mass Number
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Atomic Number
39
The atomic number
• is specific for each element
• is the same for all atoms of an element
• is equal to the number of protons in an atom
• appears above the symbol of an element in the Periodic
Table
Atomic Number
Symbol
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11
Na
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Atomic Number = Protons in Atom
40
For example, atomic number = number of protons:
• Atomic number H is 1; every H atom has one proton
• Atomic number of C is 6; every C atom has six protons
• Atomic number of Cu is 29; every Cu atom has 29
protons
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Atomic Number = Protons in Atom
41
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Atoms Are Neutral
42
For neutral atoms, the net charge is zero.
number of protons = number of electrons
Aluminum has 13 protons and 13 electrons. The net
(overall) charge is zero.
13 protons (13+) + 13 electrons (13–) = 0
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Learning Check
43
Use the periodic table to fill in the atomic number, number of
protons, and number of electrons for each of the following
elements:
Element Atomic
Number
N
Protons
Electrons
Zn
S
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Solution
44
Use the periodic table to fill in the atomic number, number of
protons, and number of electrons for each of the following
elements:
Element Atomic
Number
N
7
Protons
Electrons
7
7
Zn
30
30
30
S
16
16
16
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Mass Number
45
The mass number
• represents the number of particles in the nucleus
• is equal to the number of protons + the number of neutrons
• is always a whole number
• does not appear in the periodic table
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Composition of Some Atoms of
Different Elements
46
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Study Tips: Protons and Neutrons
47
Number of protons = atomic number
Number of protons + neutrons = mass number
Number of neutrons = mass number – atomic number
Note: Mass number is given for specific isotopes only.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Learning Check
48
An atom of lead (Pb) has a mass number of 207.
A. How many protons are in the nucleus?
B. How many neutrons are in the nucleus?
C. How many electrons are in the atom?
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Solution
49
An atom of lead (Pb) has a mass number of 207.
A. How many protons are in the nucleus?
atomic number = 82; number protons = 82
B. How many neutrons are in the nucleus?
mass number – number protons = number neutrons
207 – 82 = 125 neutrons
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Solution
50
An atom of lead (Pb) has a mass number of 207.
C. How many electrons are in the atom?
An atom is neutral, which means that the
number of electrons is equal to the number of
protons. An atom of Pb has 82 protons and
82 electrons.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Chapter 3
Atoms and Elements
51
3.5
Isotopes and Atomic Mass
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Isotopes
52
Isotopes
• are atoms of the same element
• have different mass numbers
• have same number of protons but different numbers of
neutrons
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Atomic Symbols and Subatomic
Particles
53
Examples of number of subatomic particles for atoms:
Atomic symbol
16
31
O
8
8 p+
8n
8 e-
P
15
15 p+
16 n
15 e-
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65
Zn
30
30 p+
35 n
30 eCopyright © 2012 by Pearson Education, Inc.
Atomic Symbols for Isotopes of
Magnesium
54
Mass Numbers
24
12
Mg

25
12
Mg
26
12
Mg

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Atomic Symbols for Isotopes of
Magnesium
55
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Learning Check
56
Naturally occurring carbon consists of three isotopes: 12C,
13C, and 14C. State the number of protons, neutrons, and
electrons in each of the following:
Isotope
12C
13C
14C
protons
neutrons
electrons
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Solution
57
Naturally occurring carbon consists of three isotopes: 12C,
13C, and 14C. State the number of protons, neutrons, and
electrons in each of the following:
Isotope
12C
13C
14C
protons
6
6
6
neutrons
6
7
8
electrons
6
6
6
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Learning Check
58
Write the atomic symbols for atoms with the following
subatomic particles:
A. 8 protons 8 neutrons 8 electrons
B. 17 protons 20 neutrons 17 electrons
C. 47 protons 60 neutrons 47 electrons
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Solution
59
Write the atomic symbols for atoms with the following
subatomic particles:
16
A. 8 protons 8 neutrons 8 electrons
O
8
B. 17 protons 20 neutrons 17 electrons

C. 47 protons 60 neutrons 47 electrons
37
17
Cl
107
47
Ag


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Learning Check
60
1. Which of the pairs are isotopes of the same element?
2. In which of the pairs do both atoms have 8 neutrons?
15
A. 8
B.
12
6
C.
15
7


X
15
7
X
X
14
6
X
X
16
8
X
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Learning Check
61
1. Which of the pairs are isotopes of the same element?
12
6
B.
X
14
6
X
2. In which of the pairs do both atoms have 8 neutrons?
C.


15
7
X
16
8
X
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Atomic Mass
62
Atomic mass is the
• weighted average of all
naturally occurring
isotopes of that element
• number on the periodic
table below the chemical
symbol with two decimal
places
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Calculating Atomic Mass
63
To calculate atomic mass,
• use an experimental percent abundance of each isotope
of the element
• multiply the percent abundance by the atomic mass of
that isotope
• sum the total mass of each isotope
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Calculating Atomic Mass
64
To calculate atomic mass of Cl, use experimental data for
both isotopes of Cl:
Isotope atomic mass x % abundance
35Cl
37Cl
34.97 amu x 75.76 = 26.49 amu
100
36.97 amu x 24.24 = 8.962 amu
100
Atomic mass of Cl = 35.45 amu
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The Atomic Mass of Some Elements
65
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Learning Check
66
Lithium consists of two naturally occurring isotopes, 6Li and 7Li.
Use the periodic table to predict which isotope is the most
prevalent one.
Periodic table atomic mass of lithium is 6.941 amu.
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Solution
67
Lithium consists of two naturally occurring isotopes, 6Li and 7Li.
Use the periodic table to predict which isotope is the most
prevalent one.
Periodic table atomic mass of lithium is 6.941 amu.
6Li and 7Li
Since the total atomic mass of 7Li is closer to 7, the mass number
of 7Li, the most prevalent isotope is 7Li.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Learning Check
68
Gallium is an element found in lasers used in compact disc
players. In a sample of gallium, there is 60.10% of 69Ga
(atomic mass 68.926) atoms and 39.90% of 71Ga (atomic mass
70.925) atoms.
What is the atomic mass of gallium?
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Solution
69
69Ga
68.926 amu x 60.10 = 41.42 amu (from 69Ga)
100
71Ga
70.925 amu x 39.90 = 28.30 amu (from 71Ga)
100
Atomic mass Ga = 69.72 amu
31
Ga
69.72
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Chapter 3
Atoms and Elements
70
3.6
Electron Energy Levels
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Electromagnetic Spectrum
71
The electromagnetic spectrum shows the arrangement of
wavelengths of electromagnetic radiation, with the visible
range from 700 to 400 nm.
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Elements Have a Unique Atomic
Spectrum
72
When light from an element that is heated passes through a
prism, it separates into a unique set of distinct lines of color
called an atomic spectrum.
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Electron Energy Levels
73
Energy levels
• are assigned numbers n = 1, 2, 3, 4, and so on
• increase in energy as the value of n increases
• are like the rungs of a ladder, with the lower energy
levels nearer the nucleus
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Energy Levels
74
Energy levels have a maximum number of electrons equal
to 2n2.
Energy level
n=1
n=2
n=3
Maximum number of electrons
2(1)2 = 2(1) = 2
2(2)2 = 2(4) = 8
2(3)2 = 2(9) = 18
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Changes in Electron Energy Level
75
• Electrons move to a higher energy level when it absorbs
energy.
• When electrons fall back to a lower energy level, light is
emitted.
• The energy emitted or absorbed is equal to the
differences between the two energy levels.
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Changes in Electron Energy Level
76
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Electron Arrangements in Period 1
77
Period 1
H
1 electron in 1st energy level.
He
2 electrons in 1st energy level.
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Electron Arrangements in Period 2
78
Period 2
Energy Level
Li
Be
B
C
N
O
F
Ne
1st
2
2
2
2
2
2
2
2
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2nd
1
2
3
4
5
6
7
8
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Electron Arrangements in Period 3
79
Period 3
Energy Level
Na
Mg
Al
Si
P
S
Cl
Ar
1st
2
2
2
2
2
2
2
2
2nd
8
8
8
8
8
8
8
8
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3rd
1
2
3
4
5
6
7
8
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Electron Arrangements in Period 4
80
Period 4
Energy Level
1st
2nd
3rd
4th
K
Ca
2
2
8
8
8
8
1
2
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Electron Arrangements Beyond 20
81
Energy Level 1st
2nd
3rd
4th
5th
6th
7th
Number of
Electrons
8
18
32
32
18
8
2
Electron arrangements are written as:
O = 2,6
P = 2,8,5
Ca = 2,8,8,2
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Learning Check
82
Write the electron arrangement for the following elements:
C
Si
O
N
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Solution
83
Write the electron arrangement for the following elements:
C
=
2,4
Si
=
2,8,4
O
=
2,6
N
=
2,5
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Chapter 3
Atoms and Elements
84
3.7
Trends in Periodic Properties
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Group Number and Valence Electrons
85
For representative elements in Groups 1A–8A, chemical
properties are due to the number of valence electrons.
Valence electrons are the number of electrons in the outermost
energy level.
The group number gives the number of valence electrons for
the representative elements.
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Group Number and Valence Electrons
86
Group Number
1A
2A
3A
4A
5A
6A
7A
8A
# Valence Electrons
1
2
3
4
5
6
7
8
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Electron-Dot Symbols
87
Electron-dot symbols
• are also known as Lewis structures
• represent the valence electrons as dots placed on sides
of symbol
For example, Al = 2,8,3
Three valence electrons are represented as dots:
Al
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Electron-Dot Symbol for Mg
88
Possible electron-dot symbols for magnesium, with the
electron arrangement of 2,8,2,
• include 2 valence electrons, represented as dots
• can be drawn in more than one way
Mg
Mg
Mg
Mg
Mg
Mg
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Electron-Dot Symbol for Mg
89
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Electron-Dot Symbols for Selected
Elements
90
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Learning Check
91
Write the electron-dot symbol for each of the following
elements: Cl, C, N.
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Solution
92
Write the electron-dot symbol for each of the following
elements:
Cl
C
N
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Atomic Size
93
Atomic size
• is determined by the atom’s atomic radius, the distance
between nucleus and outermost electrons
• increases for representative elements from top to bottom
of the periodic table
• decreases within a period due to increased number of
protons in nucleus
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Atomic Size
94
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Atomic Size
95
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Ionization Energy
96
Ionization energy
• is the energy required to remove one of the outermost
electrons from an atom
Na(g) + energy (ionization)  Na+(g) + e−
• decreases down a group, increases across a period from
left to right
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Ionization Energy
97
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Metallic Character
98
An element with metallic character is one that loses
electrons easily.
Metallic character
• is more prevalent in metals on left side of periodic table
• is less for nonmetals on right side of periodic table that
do not lose electrons easily
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Metallic Character
99
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Summary of Trends in Periodic Table
100
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Learning Check
101
Given the following elements:
C
N
Cl
Which is the largest atom?
Which has the highest ionization energy?
Which belongs to Group 5A?
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
102
Given the following elements:
C
Which is the largest atom?
Which has the highest ionization energy?
Which belongs to Group 5A?
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
N
Cl
C
Cl
N
Copyright © 2012 by Pearson Education, Inc.