Why do lithium and sodium corrode so easily?
$$\ce{2Li + 2H2O -&gt; 2LiOH + H2}$$
$$\ce{2LiOH + CO2 -&gt; Li2CO3 + H2O}$$ 
$$\ce{4Li + O2 -&gt; 2Li2O}$$ 
$$\ce{Li2O + CO2 -&gt; Li2CO3}$$
$$\ce{6Li + N2 -&gt; 2Li3N}$$
Lithium and sodium are reacting with the gases in the air; a destructive physical process.