The bond formation is accompanied by the lowering of the energy of the system. In the case of the atoms where electron transfer is to favoured energy consideration, a chemical bond may be formed in some manner which may also lead to lowering the energy of the system.
When an atom or molecule is adsorbed on a surface new electronic states are formed due to the bonding to the surface. The nature of the surface chemical bond will determine the properties and reactivity of the adsorbed molecule.
The atomic orbitals overlap on the bond formation and the larger the overlap, the stronger is the bond. This localized picture of a chemical bond is, in a way, equivalent to the delocalized picture given by the molecular orbital theory.
For example, in a CH4 molecule, there will be a sharing of electrons between carbon and hydrogen atoms. These type of bonds is known as covalent bonds. Generally, non-metals form a chemical bond by sharing electrons with each other. An ionic bond is formed as a result of the transference of electrons from one atom to another.