Why do alkali metals react with water?

1 Answer
Oct 20, 2015

The alkali metals are all strongly influenced by their #ns^1# valence electron configuration. They are strongly reducing, and very soft or liquid at RT.


Given the #ns^1# configuration, the metals are strongly reducing. Their reaction with water reflects this:

#M(s) + H_2O(l) rarr M(OH)(aq) + 1/2H_2(g)#

They also react quantitatively with liquid ammonia (another protic solvent):

#M(s) + NH_3(l) rarr M(NH_2)(aq) + 1/2H_2(g)#

Both in water and (longer-lived) in ammonia, a solvated electron #e^-#, is invoked, and this species is responsible for the brilliant blue colour observed in liquid ammonia.

The #ns^1# configuration may also be held responsible for the softness and ductility of the alkali metals, as their propensity to undergo metallic bonding is reduced with respect to other metals, and their melting/boiling points are low. Many labs still have a sodium press, a die with a threaded ram, which can drive the metal through a small hole to produce metres of sodium ribbon.