Why the bond in MgH2 is covalent rather ionic as Mg is a metal of 2nd group and hydrogen can accept electron then why the bond is covalent

@ bhanu 
covalent charecter usually comes from having a cation that is very small reacting with a relativly large anion . when u have small highly charged cation , you can say that the ion has polarising power , and polarising power comes from the ratio between the size charge and radius being correct . if a cation has a high polarising power , it pulls the large electron clouds from the anion forming a bond that is at least partially covalent . 
as far as mgh2 is concerned mg is small relativly high charge ion and the h- ion is relativly large , 
so, u will end up getting something as covalent here . 
HOPE IT CLEARS YOUR DOUBT 
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