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CH 3 Atoms and elements 1

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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

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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

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Some Elements and Their Names
3

Names come from:
• planets
• mythological figures
• minerals
• colors
• geographic locations
• famous people

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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

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Chemical Symbols from Latin Names
5

Ag
Au

silver, from argentum
gold, from aurum

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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

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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

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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

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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

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Chapter 3
Atoms and Elements
10

3.2
The Periodic Table

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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

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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

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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

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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

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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

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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.

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Rutherford's Gold Foil Experiment
32

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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
electrons
B. has a positive charge
protons
C. has mass but no charge
neutrons

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Chapter 3
Atoms and Elements
38

3.4
Atomic Number and Mass Number

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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

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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

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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.

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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?

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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

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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.

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Chapter 3
Atoms and Elements
51

3.5
Isotopes and Atomic Mass

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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

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Atomic Symbols and Subatomic
Particles
53

Examples of number of subatomic particles for atoms:
Atomic symbol
16

31

O
8

P
15

8 p+
8n
8 e-

65

Zn
30

15 p+
16 n
15 e-

30 p+
35 n
30 e-

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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,
13
C, and 14C. State the number of protons, neutrons, and
electrons in each of the following:
Isotope

C

12

C

13

C

14

protons
neutrons
electrons

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Solution
57

Naturally occurring carbon consists of three isotopes: 12C,
13
C, and 14C. State the number of protons, neutrons, and
electrons in each of the following:
Isotope

C

12

C

13

C

14

protons

6

6

6

neutrons

6

7

8

electrons

6

6

6

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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

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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

37
17


C. 47 protons 60 neutrons 47 electrons

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?
A. 15
8

B. 12
C.




6

15
7

X

15
7

X

X

14
6

X

X

16
8

X

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Learning Check
61





1. Which of the pairs are isotopes of the same element?
B.

12
6

X

15
7

X

14
6

X

2. In which of the pairs do both atoms have 8 neutrons?
C.





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
Cl

35

Cl

37

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.
6
Li and 7Li
Since the total atomic mass of 7Li is closer to 7, the mass number of 7Li, the most prevalent isotope is 7Li.

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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

Ga
68.926 amu x 60.10 = 41.42 amu (from 69Ga)
100
71
Ga
70.925 amu x 39.90 = 28.30 amu (from 71Ga)
100
Atomic mass Ga = 69.72 amu
69

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
2
Be
2
B
2
C
2
N
2
O
2
F
2
Ne
2

1st
1
2
3
4
5
6
7
8

2nd

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Electron Arrangements in Period 3
79

Period 3
Energy Level
Na
2
Mg
2
Al
2
Si
2
P
2
S
2
Cl
2
Ar
2

1st
8
8
8
8
8
8
8
8

2nd

3rd

1
2
3
4
5
6
7
8

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Electron Arrangements in Period 4
80

Period 4
Energy Level

1st

K
Ca

8
8

2
2

2nd
8
8

3rd

4th

1
2

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Electron Arrangements Beyond 20
81

Energy Level

1st

Number of
Electrons 2 8

18

2nd
32

3rd

4th

32

5th

18

6th

7th

8

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

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition

Copyright © 2012 by Pearson Education, Inc.

Atomic Size
94

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition

Copyright © 2012 by Pearson Education, Inc.

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 N Cl
Which is the largest atom?
C
Which has the highest ionization energy? Cl
Which belongs to Group 5A?
N

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition

Copyright © 2012 by Pearson Education, Inc.

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