The Foundations of Chemistry

the metals are dropped into water. The large amounts of heat evolved provide the acti-
vation energy to ignite the hydrogen. The elements also react with water vapor in the air
or with moisture from the skin.

2K(s)
2H 2 O(
)88n2[K
(aq)
OH(aq)]
H 2 (g) H^0 390.8 kJ/mol rxn

Alkali metals are stored under anhydrous nonpolar liquids such as mineral oil.
As is often true for elements of the second period, Li differs in many ways from the
other members of its family. Its ionic charge density and electronegativity are close to
those of Mg, so Li compounds resemble those of Mg in some ways. This illustrates the
diagonal similaritiesthat exist between elements in successive groups near the top of the
periodic table.

IA IIA IIIA IVA

Li Be B C

Na Mg Al Si

Lithium is the only IA metal that combines with N 2 to form a nitride, Li 3 N. Magnesium
readily forms magnesium nitride, Mg 3 N 2. Both metals readily combine with carbon to
form carbides, whereas the other alkali metals do not react readily with carbon. The solu-
bilities of Li compounds are closer to those of Mg compounds than to those of other IA
compounds. The fluorides, phosphates, and carbonates of both Li and Mg are only slightly
soluble, but their chlorides, bromides, and iodides are very soluble. Both Li and Mg form
normal oxides, Li 2 O and MgO, when burned in air at 1 atmosphere pressure. The other
alkali metals form peroxides or superoxides.
The IA metal oxides are basic. They react with water to form strong bases.

Na 2 O(s)
H 2 O(
)88n2[ Na
(aq)
OH(aq)]

K 2 O(s)
H 2 O(
)88n2[ K
(aq)
OH(aq)]

23-2 Reactions of the Group IA Metals 923

TABLE 23-2 Some Reactions of the Group IA Metals

Reaction Remarks

4M
O 2 88n2M 2 O Limited O 2

4Li
O 2 88n2Li 2 O Excess O 2 (lithium oxide)

2Na
O 2 88nNa 2 O 2 (sodium peroxide)

M
O 2 88nMO 2 MK, Rb, Cs; excess O 2 (superoxides)

2M
H 2 88n2MH Molten metals

6Li
N 2 88n2Li 3 N At high temperature

2M
X 2 88n2MX Xhalogen (Group VIIA)

2M
S88nM 2 S Also with Se, Te of Group VIA

12M
P 4 88n4M 3 P

2M
2H 2 O88n2MOH
H 2 K, Rb, and Cs react explosively

2M
2NH 3 88n2MNH 2 
H 2 With NH 3 (
) in presence of catalyst;

with NH 3 (g) at high temperature

(solutions also contain M

solvated e)

Sodium reacts vigorously with water.

2Na(s)
2H 2 O(
)88n

2[Na
(aq)
OH(aq)]
H 2 (g)

The indicator, phenolphthalein, was

added to the water. As NaOH forms,

the solution turns pink.