giant metallic bond

Fist of all, there is no such bond called giant metallic bond. There are giant metallic structure, and metallic bond.

In a metal or an alloy, the metal atoms are held together by metallic bonds. The metallic bonds are due to the delocalization of the outermost shell electrons of the metal atoms. The strength of metallic bonds depends on :
(1) The greater the number of delocalized electrons for each atom, the stronger the metallic bond.
(2) The shorter the atomic radii of the metal atoms, the stronger the metallic bond.

In Group I metals, there are only one delocalized electron for each atom, and thus their metallic bonds are weak.

In Group III metals, there are three delocalized electrons for each atom. Besides, Group III metal has a smaller atomic size than Group I metal in the same period. Therefore, Group III metals have stronger metallic bonds than Group I metals.

2006-12-14 22:16:43 補充：
The term 「mobile electrons」 cannot be used to replace the term 「delocalized electrons」. All electrons in atoms must be mobile.

The number of mobile electrons in the electron sea is larger, it gives rise to stronger metallic bond.