ionic compounds are held together by electrostatic attraction,
producing highly ordered crystals to reduce repulsion between
similarly charged ions while maximizing attraction between
oppositely charged ions. this explains the large energy required to
break the bonds in ionic compounds.
metals are held together by metallic bonding (can't remember if
you can use this phrase =P), which is the electromagnetic
interaction between the delocalized electrons and metallic ions.
this bonding however is nondirectional which explains why they are
malleable and ductile. this explains why their lattice structure,
although present, is weaker than in ionic compounds.
(long time since i touched chemistry, just what i remember =P
just take this as a guideline to find the proper explanation in
your notes and stuff)