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EXAMPLE
Problem 1
ATOMIC NUMBER
Complete the following table.
Composition of Several Elements
Element
Atomic Number
Protons
Electrons
a.
Pb
82
b.
8
c.
30
1
ANALYZE THE PROBLEM
Apply the relationship among atomic number, number of protons, and number of electrons to
complete most of the table. Then, use the periodic table to identify the element.
Known
Unknown
a.
element
=
Pb, atomic number
=
82
a.
number of protons
(
N
p
)
, number of electrons
(
N
e
)
=
?
b.
number of protons
=
8
b.
element,
atomic number
(
Z
),
N
e
=
?
c.
number of electrons
=
30
c.
element,
Z
,
N
p
=
?
2
SOLVE FOR THE UNKNOWN
a.
number of protons
=
atomic number
Apply the atomic-number relationship.
N
p
=
82
Substitute atomic number
=
82.
number of electrons
=
number of protons
N
e
=
82
The number of protons and the number of electrons is 82.
b.
atomic number = number of protons
Apply the atomic-number relationship.
Z
=
8
Substitute number of protons
=
8.
number of electrons
=
number of protons
N
e
=
8
The atomic number and the number of electrons is 8.
Consult the periodic table to identify
The
element
is
oxygen (0).
the element.
c.
number of protons
=
number of electrons
Apply the atomic-number relationship.
N
p
=
30
Substitute number of electrons
=
30.
atomic number
=
number of protons
Z
=
30
The atomic number and the number of protons is 30.
Consult the periodic table to identify
The
element
is
zinc
(Zn).
the element.
3
EVALUATE THE ANSWER
The answers agree with atomic numbers and element symbols given in the periodic table.
PRACTICE
Problems
11.
How many protons and electrons are in each atom?
a.
radon
b.
magnesium
12.
An atom of an element contains 66 electrons. Which element is it?
13.
An atom of an element contains 14 protons. Which element is it?
14. CHALLENGE
Do the atoms shown in the figure to the right have
the same atomic number?
C04_024A
10n
9p
9n
9e
ADDITIONAL PRACTICE
92
Module 3 • The Structure of the Atom