Why does Beryllium not react with water?

1. Among the alkaline earth metals (Group 2 elements), Beryllium has the smallest atomic size and the highest ionization energy.
2. The high ionization energy indicates that it is very difficult for Beryllium to donate its valence electrons to the hydrogen atoms of a water molecule. This inhibits Beryllium's reactivity towards the water.
3. Another reason is that beryllium's surface is coated with a thin layer of Beryllium oxide ($\mathrm{BeO}$) which prevents it from reacting with water at lower temperatures.
4. At temperatures of around 700-750 °C, the oxide layer may break and Beryllium may react with steam to form Beryllium oxide and liberate hydrogen gas (the validity of this reaction is still disputed).

$\mathrm{Be}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)\stackrel{700°\mathrm{C}}{\to }\mathrm{BeO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$