Modern inorganic chemistry

GROUPS I AND II 135

Table 6.5

SUMMARY OF THE CHEMISTRY OF LITHIUM

Li Na K Rb Cs

Element Hard metal Soft metals

Hydroxide Not a strong base Strong bases

Fluoride Only slightly soluble Readily soluble in water

in water

Chloride Slightly hydrolysed Not hydrolysed

in hot solution

Bromide Soluble in many Insoluble in most organic solvents

and iodide organic solvents • —

Carbonate Evolves carbon Stable to heat

dioxide on heatine •

energies. The insolubility of lithium fluoride results from the high
lattice energy which in this case is not exceeded by the combined
hydration energies. Other Group I fluorides dissolve since the lattice
energies are smaller and are exceeded by the combined hydration
energies.
In this discussion, entropy factors have been ignored and in
certain cases where the difference between lattice energy and
hydration energy is small it is the entropy changes which determine
whether a substance will or will not dissolve. Each case must be
considered individually and the relevant data obtained (see Chapter
3), when irregular behaviour will often be found to have a logical
explanation.
The abnormal properties of lithium and beryllium are summarised
in Tables 6.5 and 6.6.

Table 6.6

SUMMARY OF THE CHEMISTRY OF BERYLLIUM

Hydroxide

Fluoride

Chloride

Be

Amphoteric

Soluble in water

Partly covalent

Me

Sparingly

Ca -- Ba

Basic

soluble to soluble in water

I -. n K

Other compounds Often covaien!