Properties of alkali metals
Alkali metals are Group I metals on the Periodic Table and have a 1 electron in the outer shells of each of their atom. Alkali metals belong to the s-block metals of the Periodic Table and they only have one electron in their outer shell.
Examples of alkali metals are:
- lithium (Li)
- sodium (Na)
- potassium (K)
- rubidium (Rb)
- caesium (Cs)
- francium (Fr)
Physical properties of alkali metals
- alkali metals general have a silvery white appearance except for caesium which is golden yellow.
- they have low melting and boiling points, compared with most metals.
- their melting points decrease down the group.
- they are all soft and can be cut with a knife.
- the softness of alkali metal increases down the group with caesium being the softest of the alkali metals.
- they are good conductors of heat and electricity.
- they are less dense to the point that they float on water, while reacting with it.
- their densities increase down the group.
|Metal||Density in g/cm3||Melting point in °C|
Chemical properties of alkali metals
alkali metals are generally very reactive
they oxidise easily when exposed to air, forming an oxide, peroxide or superoxide depending on the metal. E.g:
- 4Li + O2 → 2Li2O (Lithium oxide)
- 2Na + O2 → Na2O2 (Sodium peroxide)
- K + O2 → KO2 (Potassium superoxide)
the reactivity of alkali metals increases within the group, with lithium being the least reactivity and caesium the most reactive.
alkali metals react violently with water forming a metal hydroxide and hydrogen. E.g:
2Li(s) + 2H2O → 2LiOH + H2(g)
they react with halogens to form metal halides which are very soluble in water and partly soluble in organic solvents. E.g:
2Na + Cl2 → 2NaCl (Sodium Chloride)