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Chapter 3 Atoms and Elements
1
Elements are pure substances that cannot be separated into simpler substances by ordinary
laboratory processes
•
Elements are the building blocks of matter
• Chemistry:
Elements
are listed
in Organic,
the Periodic
Table
An Introduction
to General,
and Biological
Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
•
Periodic Table of Elements
2
Objective
You must identify:
• Alkali and Alkaline metals
• Halogens
• Noble Gases
• Representative Elements
• Transition Elements
• Post Transition Metals
• Group numbers, location
• Period numbers, location
• Metals
• Nonmetals
• Metalloids
• Solids, Liquids and gases
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Classification of Elements
3
Group numbers
use letter A for representative elements
(Groups 1A – 8A)
use letter B for transition elements
(also called transition metals)
(Groups 1B – 8B)
3B
4B
5B
6B
7B
8B
8B
8B
1B
Transition Metals
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
2B
Post
Transition
Metals
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Learning Check
4
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
5
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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Metals, Nonmetals and Metalloids Properties
6
Nonmetals
Metals
Metals
zig-zag line
• are shiny and ductile
• are good conductors of heat and electricity
Nonmetals
metals
• 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
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
nonmetals
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Comparing Metal, Nonmetal, and
Metalloid elements
7
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Learning Check
8

Identify each of the following elements as a metal, nonmetal,
or metalloid.
A. sodium
B. chlorine
C. silicon
D. iron
E. carbon
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Solution
9

Identify each of the following elements as metal, nonmetal,
or metalloid.
A. sodium
B. chlorine
C. silicon
D. iron
metal
nonmetal
metalloid
metal
E. carbon
nonmetal
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Learning Check
10
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
11
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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Atoms and the Atomic Theory
12
The Atom
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Dalton's Atomic Theory
13
In Dalton's atomic theory:
• Atoms are tiny particles of matter
• Atoms of an element are similar to each
other and different from other elements
• Atoms of two or more different elements
combine to form compounds
• Atoms are rearranged to form new
combinations in a chemical reaction
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Subatomic Particles Electrical Charges
14
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
(how was the existence of the atomic nucleus determined)
15
In Rutherford’s gold foil experiment:
•
Positively charged particles were aimed at atoms of gold
•
The positive particles went mostly straight through the atoms
•
However the positive particles were deflected 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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Structure of the Atom
16
 An atom consists of a nucleus that contains the protons and neutrons
 The electrons are moving in a large, empty space around the nucleus
(called “the electronic cloud”)
Electronic cloud
neutron
proton
electron
Nucleus
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Subatomic Particles in the Atom
17
In SI units, the mass of the proton is 1.673 x 10−24 g
and the mass of the neutron is 1.675 x 10−24 g
A more common unit to express subatomic particle masses is the “atomic mass unit”
 1 atomic mass unit (amu) is equal to 1/12 of the mass of the carbon atom.
 1 atomic mass unit (amu) is equivalent to 1.6605 x 10−24 g (in SI units)
 a proton has a mass of 1.007 amu (equal to 1.673 x 10−24 g in SI units)
 a neutron has a mass of 1.008 amu (equal to 1.675 x 10−24 g in SI units)
 an electron has a very small mass, 0.00055 amu (considered negligible)
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Learning Check
18

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
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Solution
19

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
20
The Atomic Number
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Atomic Number
21
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
22
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
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Atoms are Neutral
23
For atoms, the net charge is zero.
number of protons = number of electrons
Qty (+) charges = Qty (-) charges
Aluminum has 13 protons and 13 electrons.
The net (overall) charge in Aluminum 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
24
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
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Solution
25
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
26
The mass number
• represents the number of subatomic 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
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Composition of Some Atoms of
Different Elements
27
Not found directly in the
periodic table
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Study Tips: Protons and Neutrons
28
Number of protons = atomic number
Number of electrons = number of protons = atomic number
Number of protons + neutrons = mass number
Number of neutrons = mass number – atomic number
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Learning Check
29
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
30
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
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.
Therefore 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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Isotopes and Atomic Mass
31
Isotopes
•
are atoms within the same element that have
different mass numbers
•
have same number of protons but different
numbers of neutrons
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Atomic Symbols are used to represent Isotopes
Example: Isotopes of Magnesium
32
Mass Numbers
24
12
Mg
Mg-24
25
12
Mg
Mg-25
26
12
Mg
Mg-26
Atomic Symbols: How Isotopes are represented


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Atomic Symbols and Subatomic Particles
33
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
34
How does Magnesium shows
in the Periodic Table?
12
Mg
24.31
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Atomic
Number
Atomic
Mass (amu)
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Learning Check
35
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
36

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
16
8
O
37
17
Cl
107
47
Ag

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
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Learning Check
37
1. Which of the pairs are isotopes of the same element?
A.
15
8
B.
12
6
X
15
7
X
X
14
6
X
16
8
X

15 X
C.
7

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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
Solution
38
1. Which of the pairs are isotopes of the same element?
B.
12
6
X
14
6
X

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Average Atomic Mass
39

•
•
Average Atomic mass (is sometimes referred to
s the “atomic mass”)
The average atomic mass is the weighted average
of all naturally occurring isotopes of that element
The average atomic mass is the number shown on
the periodic table below the chemical symbol
with two decimal places
Atomic
Number
17
Cl
35.45
Atomic
Mass
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Calculating Average Atomic Mass
40
To calculate the average 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
Examples: Na and Cl
11
17
Na
Cl
22.99
35.45
Objective: Using the periodic table, identify the Atomic Mass.
(Atomic Mass calculation from experimental data will not be evaluated in this course)
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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How is the Average Atomic Mass calculated?
Example: How is the average atomic mass of chlorine calculated?
41

To calculate the atomic mass of Cl, we use
experimental data for both isotopes of Cl:
Isotope
atomic mass x % abundance
35Cl
34.97 amu
x 75.76 % = 26.49 amu
37Cl
36.97 amu
x 24.24 % =
8.962 amu
Atomic mass of Cl = 26.49 amu + 8.962 amu
Atomic mass of Cl = 35.45 amu
Objective: Using the periodic
table, identify the Atomic Mass.
(Atomic Mass calculations from
experimental data will not be
evaluated in this course)
17
This will be the Atomic Mass value
which is shown in the Periodic Table
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Cl
35.45
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The Atomic Mass of Some Elements
42
Li-7
C-12
O-16
F-19
S-32
Cu-63
The mass number (for the prevalent isotope) in each element, can be
determined by rounding off the Atomic Mass to the nearest whole number.
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Learning Check
43

Lithium consists of two naturally occurring isotopes, Li-6 and Li-7.

Use the periodic table to predict which isotope is the most prevalent one.

What is the mass number of the most prevalent (most abundant) isotope?
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Solution
44

Lithium consists of two naturally occurring isotopes, Li-6 and Li-7.

Use the periodic table to predict which isotope is the most prevalent one.

What is the mass number of the most prevalent (most abundant) isotope?
The periodic table atomic mass of lithium is 6.941 amu.
3
Li
6.941
Since the atomic mass of Li is closer to 7, the most prevalent isotope is Li-7.
The mass number of the most prevalent (must abundant) isotope is 7
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Electron Energy Levels
45
• Energy levels are assigned numbers n = 1, 2, 3, 4, and so on
• The electrons increase in energy as the Energy Level number n increases
• The lower energy levels are nearer the nucleus
12
Example: Magnesium
Mg
24.31
n=1
neutron
proton
n=2
n=3
electron
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Electron Energy Levels
46
Energy levels have a maximum number of electrons equal to 2n2.
Energy level
Maximum number of electrons
n=1
2(1)2
= 2(1) = 2
n=2
2(2)2
= 2(4) = 8
n=3
2(3)2
= 2(9) = 18
12
Mg
24.31
n=1
neutron
proton
Example: Magnesium
n=2
n=3
electron
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Changes in Electron Energy Level
47
• Electrons move to a higher energy level when it
absorbs energy.
• When electrons fall back to a lower energy level,
light is emitted.
Example: Magnesium
12
• The energy emitted or absorbed is equal to the
differences between the two energy levels.
n=1
neutron
proton
Mg
24.31
n=2
n=3
electron
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Electron Arrangements in Period 1
48
Period 1
Energy Level
1st
(there is only one energy level in these two atoms)
H
1 electron
He
2 electrons
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Electron Arrangements in Period 2
49
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
50
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
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
3rd
1
2
3
4
5
6
7
8
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Electron Arrangements in Period 4
51
Period 4
Energy Level
1st
2nd
3rd
4th
K
Ca
2
2
8
8
8
8
1
2
Electron arrangements are written as indicated below:
Examples for oxygen, phosphorous and calcium:
O = 2-6
P = 2-8-5
Ca = 2 - 8 - 8 - 2
Electron arrangements above atomic number 20:
Beyond the first 20 elements, the electron arrangements become
more complicated and will not be covered in this course.
Reference: Syllabus, page 5, Competency 2, letter g.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Learning Check
52
Write the electron arrangement for the following elements:
C
Si
O
N
K
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Solution
53
Write the electron arrangement for the following elements:
C = 2-4
Si = 2 - 8 - 4
O = 2-6
N = 2-5
K = 2-8-8-1
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Group Number and Valence Electrons
54

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.
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
55
Electron-dot symbols
• are also known as Lewis electron dot symbols
• dots are placed on different sides of the element
symbol to represent valence electrons
For example, Al = 2,8,3
Three valence electrons are represented as dots:
Al
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Electron-Dot Symbol for Mg
56
 Electron-dot symbols for magnesium, with the
electron arrangement of 2-8-2
• The 2 valence electrons are represented as dots
• The dots can be drawn in more than one way
• Any of the representations shown below are
acceptable:
Mg
Mg
Mg
Mg
Mg
Mg
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Electron-Dot Symbols for Selected Elements
57
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Learning Check
58
Write the electron-dot symbol for each of the following
elements: Cl, C, N.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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Solution
59
Write the electron-dot symbol for each of the following
elements:
Cl
C
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
N
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Exercises
Use the periodic table (Representative Elements) to complete the blank information below:
60
Element
name
Symb
Group
number
Period
number
Atomic
number
Ave.
Atomic
mass
Mass
number
(of most
abundant
isotope)
Atomic
Symbol
(of most
abundant
isotope)
Number
of
protons
Number
of
neutrons
(of most
abundant
isotope)
Total
number of
electrons
Number
of valence
electrons
Number
of
energy
levels
8
3
Electron
dot
symbol
Electron
arrangement
Lithium
Ca
10
13
2-8-18-7
4A
2
19
3
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Exercises
Use the periodic table (Representative Elements) to complete the blank information below:
61
Number
of
protons
Number
of
neutrons
(of most
abundant
isotope)
Total
number of
electrons
Number
of valence
Li
3
4
3
1
2
Li •
Ar
18
22
18
8
3
: Ar :
Ca
20
20
20
2
4
Ne
10
10
10
8
2
Al
13
14
13
3
3
•
• Al •
Br
35
35
45
35
7
4
: Br
•
••
C
6
6
6
4
2
K
19
20
19
1
4
P
15
16
15
5
3
Group
number
Period
number
Atomic
number
Ave.
Atomic
mass
Mass
number
(of most
abundant
isotope)
Li
1A
2
3
6.941
7
7
3
argon
Ar
8A
3
18
39.95
40
40
18
calcium
Ca
2A
4
20
40.08
40
neon
Ne
8A
2
10
20.18
20
20
10
aluminum
Al
3A
3
13
26.98
27
27
13
bromine
Br
7A
4
35
79.90
80
carbon
C
4A
2
6
12.01
12
potassium
K
1A
4
19
39.10
39
phosphorus
P
5A
3
15
30.97
31
Element
name
Symb
lithium
Atomic
symbol
(of most
abundant
isotope)
40
20
80
12
6
39
19
31
15
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
electrons
Number
of
energy
levels
Electron
dot
symbol
••
••
•
Ca •
••
: Ne
:
••
••
•
•C•
•
K•
••
•P•
•
Electron
arrangement
2-1
2-8-8
2-8-8-2
2-8
2-8-3
2-8-18-7
2-4
2-8-8-1
2-8-5
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Atomic Size
62
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
63
Valence
electron
Nucleus
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Ionization Energy
64
Ionization energy
• is the energy required to remove one of the outermost electrons from an atom
Na + energy (ionization)
Na+
+
e−
• decreases down a group, increases across a period from left to right
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Ionization Energy
65
Higher Ionization
Energy
Ionization energy
• Ionization energy is the energy
required to remove one of the
valence electrons from an atom
• Ionization energy decreases as the
atomic size is larger, since the
valence electrons are farther away
from the nucleus attractive forces
Lower Ionization
Energy
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Summary of Trends in Periodic Table
66
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Learning Check
67
Given the following elements:
a)
C or F
b)
O or S
c)
Mg or N
(Hint: Compare N with P, then compare P with Mg)
Which is the largest atom?
Which has the highest ionization energy?
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
68
Given the following elements:
a)
C or F
b)
O or S
c)
Mg or N
Which is the largest atom?
a) C
b) S
c) Mg
Which has the highest ionization energy?
a) F
b) O
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
c) N
Copyright © 2012 by Pearson Education, Inc.