CH 3 Atoms and elements 1 
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
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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
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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. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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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 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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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 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
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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 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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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 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
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 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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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
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Atomic Size
94
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Atomic Size
95
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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
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Ionization Energy
97
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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
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Metallic Character
99
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Summary of Trends in Periodic Table
100
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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?
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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
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Atoms and Elements
1
3.1
Elements and Symbols
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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
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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
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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. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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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 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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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 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
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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
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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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 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
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 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
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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
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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
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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
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Ionization Energy
97
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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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