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)

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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.
MetalDensity in g/cm3Melting 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)

Sydney Chako

Mathematics, Chemistry and Physics teacher at Sytech Learning Academy. From Junior Secondary School to Tertiary Level Engineering Mathematics and Engineering Science.


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