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34 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 4
Atoms have no net electrical charge because they contain equal
numbers of electrons and protons. Thus, positive charges (protons)
and negative charges (electrons) balance out. Electrons, protons, and
atomic number are related as follows.
Atomic number ϭ number of protons ϭ number of electrons
Practice Problems
2. How many electrons and protons are contained in an atom of
each of the following elements?
a. arsenic
d. molybdenum
b. gold
e. polonium
c. fluorine
f. barium
3. Identify the atom containing the following number of
electrons.
a. 34
d. 61
b. 5
e. 94
c. 31
4. Identify the atom containing the following number of protons.
a. 74
d. 70
b. 20
e. 93
c. 49
5. Atoms of which element contain 18 protons and 18 electrons?
Isotopes and mass number Although all atoms of an element
have the same number of protons, most elements have atoms with
different numbers of neutrons. For example, because the atomic
number of hydrogen is one, all atoms of hydrogen must have one
proton (and one electron). However, hydrogen atoms can have
different numbers of neutrons. Approximately 99,985 out of every
100,000 naturally occurring hydrogen atoms have no neutrons.
However, the remaining 15 out of every 100,000 hydrogen atoms
have one neutron. Atoms with the same number of protons but different numbers of neutrons are called isotopes. Hydrogen has two
naturally occurring isotopes.
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