Write in brief on
(i) ionic hydrides

Explanation

i) Ionic hydrides : These are also called as saline hydrides (or) salt like hydrides.
`to` These are the hydrides formed by combining di hydrogen with s-block elements. (Electro positive elements).
`to` These are stoichiometric compounds.
Eg : `LiH,NaH,CaH_(2)` etc.
`to` NaH is formed by the direct union of Na and `H_(2)`.
`2Na+H_(2)overset(300^(@)C)to2NaH`
Physical properties : `to` These hydrides are crystalline.
`to` These hydrides are non volatile and non-conducting in solid state.
`to` These conducts electricity in moltenstate.
`to` These have high melting points.
Chemical properties :
`to` These hydrides on electrolysis, liberates dihydrogen gas at anode.
`2H^(-)toH_(2(g))+2e^(-)["Anode"]`
`to` Lithium hydride is used in the synthesis of other useful hydrides like `LiAlH_(4)andLiBH_(4)`.
`8LiH+Al_(2)Cl_(6)to2LiAlH_(4)+6LiCl`
`2LiH+B_(2)H_(6)to2LiBH_(4)`
`2NaH+B_(2)H_(6)to2NaBH_(4)`
`to` These hydrides react with acids and water vigorously and liberate dihydrogen.
`LiH+H_(2)OtoLiOH+H_(2)uarr`
ii) Interstitial hydrides : These are the hydrides formed by the reaction of hydrogen with d-block and f-block elements. These are also called as metallic hydrides.
Eg : `CrH,CrH_(2),ZnH_(2),ThH_(2)`
`to` The hydrogen of the metallic hydride occupy the intersticies of metallic lattice. Hence these are called as Interstitial hydrides.
`to` These are non-stiochiometric compounds
Eg : `TiH_(1.5-1.8),LiH_(2.87)` etc.
`to` In these hydrides law of constant composition does not found.
`to` Metals of group 7, 8 and 9 do not form hydrides and in group 6 only chromium forms hydrides.
`to` The conductivity of these hydrides is less than the parent metals.
`to` The formation of metallic-hydrides and their capacity to release hydrogen at high temperature are utilised in the purification of `H_(2)`.
`to` Some metals can accomodate a very large volume of hydrogen and acts as storage media.