Pure Covalent Bonding
Diatomic elements such as Hydrogen, exist as two atoms. In other words, the two atoms share electrons, both atoms have an equal "pull" on the shared electron ( they both have the same electronegativity ) so a pure covalent bond is also known as a " non-polar Covalent bond.
Polar Covalent Bonding
In most compounds, the two atoms forming the covalent bond have different electronativity values. The atom with the highest electronegativity attracts electrons more strongly than the other atom. This results in the atom with the higher electronegativity having a slightly negative charge and the other having a slightly positive charge. This type of bond is known as a Polar covalent bond.
Atoms with a large difference in electronegativity will sometimes form an ionic bond. An ionic does not involve sharing electrons: it occurs where electrons are transferred from one atom to another causing one atom to lose electrons ( and become postivitly charged ) and the other to gain electrons and become negativly chraged. When a metal bonds with a non-metal, an ioic bond forms as the metal has a higher electronegativity value than the non-metal. It should be remebered that some metal compounds will be covalent.
The bonding Continuum
The higher the difference in electronegativity = ionic bond …