bondings of elements....

✔ 最佳答案

Apart from ionic and covalent bonds, we also have metallic bond which only exists between metal elements. Whether it has to be the same kind of element, I am not too much sure, for example the metal alloys consists of different elements (in the case of stainless steel, carbon is also involved). In the case of semi-conductors, different theory is used to explain the structure.

In case of SO4^2-, we have to ask where this comes from. Usually under room temperature, the sulphate ion exists in aqueous solution. It can form from two differnt ways (maybe more than two but I tried to use the simple ones as examples):

H2SO4 + 2H2O to form 2H3O^1+ + SO4^2-

or

Dissolve sulphate salts (e.g. sodium sulphate) in water

For the first one, H2SO4 is a covalent compound. When it dissolves in water the O-H bonds will break heterolytically (the electron pair in the bond will stick to O to give 1-. There are two O-H bond so altogethjer to give 2- over sulphate ion). Although H2SO4 itself is stable but after it dissolves in water, it will give even more thermdynamically stable products so this reaction is favourable.

In the 2nd case, Na2SO4 is an ionic compound and should be very stable, but when it is added to water, the whole ionic structure will be broken down because thermodynamically the products are more stable.

2009-01-19 17:51:20 補充：
single covalent bond S-O X2
double covalent bond S=O X2

negative charge on each of the O of S-O

回答 (1)