Just as the hydrogen atom is represented by a Lewis diagram consisting of the atomic symbol plus a dot for the electron, H., the H₂molecule can be written as two atomic symbols separated by a pair of dots for the bonding electrons, H:H (right). A more common practice is to replace the dots by a straight line connecting the bonded atoms, H-H, but you should remember that this straight line represents a bonding pair of electrons.

From an energy standpoint, when we say two atoms are chemically bonded we mean that the two atoms close together have less energy and therefore are more stable than when separated. Energy is given off when atoms form a bond, and energy must be supplied to pull them apart:

H + H ----> H₂(energy is given off )

H₂ -----> H + H ( energy must be added )