effect implies that the elements listed in Fig. 2.31 can lose either their valence
p-electrons alone or all their valence p- and s-electrons. These elements and the
d-block metals can form different compounds, such as tin(II) oxide, SnO, and
tin(IV) oxide, SnO2, for tin. The ability of an element to form ions with different
charges is called variable valence. Formulas of some common cations are
shown in Fig. C.6.
EXAMPLE 3.1 Writing the electron confi gurations of cations
Salts of indium(III) are used in some nutritional supplements, despite known side
effects, because it is claimed that they can enhance the speed of the memory, balance
hormones, and reduce the need for sleep. However, indium(I) salts are unstable in water
and so cannot be used in the diet. If you were working in a pharmaceutical laboratory,
you would need to be able to distinguish the properties of these two ions.
Write the electron confi gurations of (a) In and (b) In3.
ANTICIPATE Because In is in Group 13, with the “generic” electron confi guration
[core]s2p1, you should expect successive loss of the p-electron and then the two s-electrons
to give the confi gurations [core]s2 and [core], respectively.
PLAN Determine the confi guration of the neutral atom from its position in the periodic
table. Remove electrons from the valence-shell p-orbitals fi rst, then from the
s-orbitals, and fi nally, if necessary, from the d-orbitals in the next-lower shell, until the
number of electrons removed equals the charge on the ion.
SOLVE
Determine the confi guration of the neutral atom.
Indium is in Group 13, Period 5. Its ground-state confi guration
is therefore [Kr]4d105s25p1.
(a) Remove the outermost electron (from the 5p orbital).
In is [Kr]4d105s2
(b) Remove the next two electrons (from the 5s orbital).
In3 is [Kr]4d10
EVALUATE As anticipated, the two confi gurations have the form [core]s2 (as in
[Kr]4d105s2) and [core] (as in [Kr]4d10).
Self-test 3.1A Write the electron confi gurations of (a) the copper(I) ion and (b) the
copper(II) ion.
[Answer: (a) [Ar]3d10, [Ar]3d9]
Self-test 3.1B Write the electron confi gurations of (a) the manganese(II) ion and
(b) the lead(IV) ion.
Related Exercises: 3.3–3.6