Appearance
All the Group 1 elements are silvery coloured metals. They are soft, and can easily be cut with a knife to expose a shiny surface which dulls on oxidation.

General Reactivity
These elements are highly reactive metals. The reactivity increases on descending the Group from Lithium to Caesium. There is a closer similarity between the elements of this Group than in any other Group of the Periodic Table.

Occurrence and Extraction
These elements are too reactive to be found free in nature. The alkali metals are so reactive they cannot be displaced by another element, so are isolated by electrolysis of their molten salts.

Physical Properties
The alkali metals are soft, with low melting and boiling temperatures. The have low densities - Lithium, Sodium and Potassium are all less dense than water. They all show weak metallic bonding as only one electron is available from each atom.

Alkali metals colour flames.

Lithium - Red
Sodium - Yellow
Potassium - Lilac
Rubidium - Red
Caesium - Blue

The ionic radii of the alkali metals are all smaller than the atomic radii. This is because the atom contains one outer electron which is lost to form the ion. The remaining electrons are all in levels closer to the nucleus. In addition, the increased effective nuclear charge attracts the remaining electrons towards the nucleus and decreases the size of the ion.

Chemical Properties
The alkali metals are all strong reducing agents. They can reduce Oxygen, Chlorine, Ammonia and Hydrogen. The reaction with Oxygen tarnishes the metals in air, so they are all stored under oil. They cannot be stored under water because they react with it to produce Hydrogen and alkali hydroxides;

2Na(s) + 2 H2O(l) è 2NaOH(aq) + H2(g)


Lithium dissolves steadily in water with effervescence; Sodium reacts more violently and can burn with an orange flame; Potassium ignites on contact with water and burns with a lilac flame; Caesium sinks in water, but the rapid generation of Hydrogen gas produces a shock wave that can shatter a glass container.

Sodium dissolves in liquid Ammonia to give a deep blue solution. This solution is used as a reducing agent. At higher concentrations the colour of the solution changes to bronze and it conducts electricity like a metal.

The chemistry of Lithium shows some anomalies. As the Li+ ion is so small it polarises anions and so introduces a covalent character to its compounds. It has some relationship to Magnesium.

Oxides
The alkali metals form ionic solid oxides of composition M2O when burnt in air. However, Sodium forms the peroxide Na2O2 as the main product, and Potassium forms the superoxide KO2, also as the main product.

Hydroxides
Alkali metal hydroxides are white ionic crystalline solids of formula MOH, and are soluble in water. They are all deliquescent except LiOH. The aqueous solutions are all strongly alkaline. They neutralise acids to form salts;

NaOH(aq) + HCl(aq) èNaCl(aq) + H2O(l)

Halides
Alkali metal halides are white ionic crystalline solids. They are all soluble in water with the exception of LiF, resulting from the strong electrostatic interactions between the small Li+ and F- ions.