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58 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 6
Practice Problems
13. For each of the following pairs, predict which atom is larger.
a. Mg, Sr
d. Ge, Br
b. Sr, Sn
e. Cr, W
c. Ge, Sn
14. Comparing elements from left to right across a period, what
general trend would you predict for the energy required to
remove a valence electron from an atom? Explain the basis for
your prediction.
Ionic radius When an atom gains or loses one or more electrons,
it becomes an ion. Because an electron has a negative charge, gaining
electrons produces a negatively charged ion, whereas losing electrons
produces a positively charged ion. As you might expect, the loss of
electrons produces a positive ion with a radius that is smaller than
that of the parent atom. Conversely, when an atom gains electrons,
the resulting negative ion is larger than the parent atom.
Practically all of the elements to the left of group 14 of the periodic table commonly form positive ions. As with neutral atoms,
positive ions become smaller moving across a period and become
larger moving down through a group. Most elements to the right of
group 14 (with the exception of the noble gases in group 18) form
negative ions. These ions, although considerably larger than the positive ions to the left, also decrease in size moving across a period.
Like the positive ions, the negative ions increase in size moving
down through a group.
Practice Problems
In the following questions, the charges of ions are indicated by
the superscript numbers and signs.
15. For each of the following pairs, predict which atom or ion
is larger.
a. Mg, Mg 2ϩ
d. Cl Ϫ , I Ϫ
b. S, S 2Ϫ
e. Na ϩ , Al 3ϩ
c. Ca 2ϩ , Ba 2ϩ
16. Predict which of the ions, Mg 2ϩ or S 2Ϫ , is larger. Explain your
prediction.
▲
58 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 6
Practice Problems
13. For each of the following pairs, predict which atom is larger.
a. Mg, Sr
d. Ge, Br
b. Sr, Sn
e. Cr, W
c. Ge, Sn
14. Comparing elements from left to right across a period, what
general trend would you predict for the energy required to
remove a valence electron from an atom? Explain the basis for
your prediction.
Ionic radius When an atom gains or loses one or more electrons,
it becomes an ion. Because an electron has a negative charge, gaining
electrons produces a negatively charged ion, whereas losing electrons
produces a positively charged ion. As you might expect, the loss of
electrons produces a positive ion with a radius that is smaller than
that of the parent atom. Conversely, when an atom gains electrons,
the resulting negative ion is larger than the parent atom.
Practically all of the elements to the left of group 14 of the periodic table commonly form positive ions. As with neutral atoms,
positive ions become smaller moving across a period and become
larger moving down through a group. Most elements to the right of
group 14 (with the exception of the noble gases in group 18) form
negative ions. These ions, although considerably larger than the positive ions to the left, also decrease in size moving across a period.
Like the positive ions, the negative ions increase in size moving
down through a group.
Practice Problems
In the following questions, the charges of ions are indicated by
the superscript numbers and signs.
15. For each of the following pairs, predict which atom or ion
is larger.
a. Mg, Mg 2ϩ
d. Cl Ϫ , I Ϫ
b. S, S 2Ϫ
e. Na ϩ , Al 3ϩ
c. Ca 2ϩ , Ba 2ϩ
16. Predict which of the ions, Mg 2ϩ or S 2Ϫ , is larger. Explain your
prediction.
▲