Chemical Properties

Overall Group 2 is less reactive than Group 1 in the same period, but here too reactivity climbs steadily down the group.

1. Reactivity towards air and water Beryllium and magnesium are both kinetically protected from oxygen and water by a thin, tenacious oxide film on their surface — although finely powdered beryllium, with its film disrupted, burns brilliantly in air to give $BeO$ and $Be_3N_2$. Magnesium, more electropositive than beryllium, likewise burns with dazzling brightness to give $MgO$ and $Mg_3N_2$. Calcium, strontium and barium have no such protective film and are readily attacked by air, forming the oxide and nitride directly; all three also react with water — with increasing vigour down the group, even in the cold — to give the hydroxide.
2. Reactivity towards the halogens At elevated temperature, every Group 2 metal combines directly with the halogens to form the halide:

   $M + X_2 \rightarrow MX_2 \quad (X = F, Cl, Br, I)$

   $BeF_2$ is best prepared not by direct combination but by thermally decomposing $(NH_4)_2BeF_4$, while $BeCl_2$ is conveniently obtained from the oxide:

   $BeO + C + Cl_2 \xrightarrow{600-800\,K} BeCl_2 + CO$

3. Reactivity towards hydrogen Every member except beryllium combines with hydrogen on heating to give the ionic-type hydride $MH_2$. Beryllium hydride will not form this way and instead has to be made indirectly, by reducing $BeCl_2$ with lithium aluminium hydride:

   $2BeCl_2 + LiAlH_4 \rightarrow 2BeH_2 + LiCl + AlCl_3$

4. Reactivity towards acids All the alkaline earth metals dissolve readily in acids, liberating hydrogen:

   $M + 2HCl \rightarrow MCl_2 + H_2$

5. Reducing nature …