There are two other very simple type of bonds found in nature. One is called metallic bond , where the valence electrons of metal atoms are shared by more than one neighboring atom. This type of bond occurs in metals only. The metal atoms are held together by a sea of electrons floating around.
Metals consist of a lattice of positive ions through which a cloud of electrons moves.
The positive ions will tend to repel one another, but are held together by the negatively charged electron cloud. The mobile electrons can transfer thermal vibration from one part of the structure to another, i.e. metals can conduct heat. They are good conductors of electricity also. Another type of bond is called the Va n der Waal s bonds , which is very weak and is usually found between gaseous compounds. In solids there is one example of a graphite crystal.