SAMPLE PROBLEM 8.8
Ranking Ions by Size
PLAN:
SOLUTION:
(a) Ca2+, Sr2+, Mg2+
(b) K+, S2-, Cl-
(c) Au+, Au3+
Compare positions in the periodic table, formation of positive and negative ions and changes in size due to gain or loss of electrons.
(a) Sr2+ > Ca2+ > Mg2+
(b) S2- > Cl- > K+
These are members of the same Group (2A) and therefore decrease in size going up the group.
These ions are isoelectronic; S2- has the smallest Zeff and therefore is the largest while K+ is a cation with a large Zeff and is the smallest.
(c) Au+ > Au3+
The higher the positive charge, the smaller the ion.
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