covalent bond 問題..................

When covalent bonds are formed between atoms, the atoms share their electrons in the outermost shell. There are two kinds of electron pairs in the outermost shell of the bonding atoms.

(1) bond pair of electrons:
They are the electrons pairs in the outermost shell of the bonding atoms that make the covalent bonds (shared by the bonding atoms).

(2) long pair of electrons:
They are the electrons pairs in the outermost shell that do not involved in the covalent bonds (are not shared by the bonding atoms.

For example, consider a NF3 molecule.

圖片參考：http://www.chem4kids.com/files/elements/compounds/ncl3_struct.gif

In the N atom, there are 3 bond pairs of electrons and 1 lone pair of electrons.
In each F atom, there are 1 bond pair of electrons and 3 lone pairs of electrons.
Consider the whole molecule. There are 3 bond pairs of electrons and 10 lone pairs of electrons.

Lone pair of electron
example : Water ( H2O )
你識畫佢個 diagram
咁就知一半
lone pair of electron 係指有 2 粒 electron ( 1 pair )係冇同其他 ion share 黎 用
咁就為之 lone pair of electron
唔明問我