What are the common physical and chemical features of alkali metals?

Physical properties:
i) metallic character: Alkali metals are highly electropositive in nature and hence, they are typical metals. the metallic character is due to low values of ionisation energies and consequently, they have a tendency to lose the valence electrons.

Low ionisation energy: The first ionisation energies of alkali metals are quite low as compared to the elements of the other groups belonging to the same period. the reason is that atoms of alkali metals are of large sizes. Therefore, the outermost electron is far away from the nucleus and can be easily removed. Within the group, ionisation energies of alkali metals decrease as we move down the group.

Low melting and boiling point: The melting and boiling points of alkali metals are very low because of the large size of their atoms due to which inter-particle forces are very weak in them. The melting and boiling points decrease on going down the group(Lithium to Cesium) as the charge density decreases because of the increase in the size of the monovalent cation.

Low electronegativity: Alkali metals have low values of electronegativity. They have very little tendency to attract the shared pair of electrons towards themselves. The electronegativity values of alkali metals decrease as we move down in the group from Li to Cs.

Soft in nature: All the alkali metals are soft and can be cut with the help of a knife.The softness of alkali metals is due to weak metallic bonding in them as the result of the large size of the atoms. As we move down the group, metallic bonding weakens and therefore, softness increases.

Density: Alkali metals have low density due to the large size of metals atoms.

Oxidation state: The alkali metals exhibit oxidation state of +1 in their compounds and strongly electropositive in character. the electropositive character increases from lithium down to caesium in the group.
Chemical properties:
Decomposition of water: The alkali metals decompose water at the ordinary temperature giving out hydrogen.
2Li+2H₂O --> 2LiOH +H₂ 

2Na +2H₂O --> 2NaOH + H₂
2K +2H₂O --> 2KOH +H₂

Reaction with oxygen: The alkali metals readily burn in oxygen or air to form their oxides
4Li +O₂ -->2LiO

combination with halogens: The alkali metals burns in halogens forming their halides

2Na +Cl₂ --> 2NaCl