Molecular compounds have low melting and boiling points. They are poor conductors of electricity and are insoluble in water but soluble in organic compounds such as alcohol and ether. Molecular compounds are formed by the sharing of pairs of electrons between atoms.
The bonds formed by the sharing of electrons are called covalent bonds. Molecular compounds can have single, double or a triple covalent bond depending on the number of pairs of electrons shared between atoms forming the bond.
The covalent bonds between atoms in a molecular compound are strong, and this gives rise to specific shapes of molecules in covalent compounds. A molecule of hydrogen is formed when two hydrogen atoms share one pair of electrons to complete the doublet of electrons in the outermost shell.
A molecule of oxygen is formed when two atoms of oxygen share a pair of electrons. The atomic number of oxygen is 8 and it has six valence electrons in its outermost shell. To complete the outer shell with eight electrons, the atom of oxygen needs two electrons. The two atoms of oxygen share one pair of electrons and form a single covalent bond. Thus, both oxygen atoms acquire the stable octet electron configuration.
Similarly, a molecule of nitrogen is formed when two atoms of nitrogen share three pairs of electrons to form a triple covalent bond between the two atoms of nitrogen.