Covalent bonds (polar covalent and pure covalent bonds)

Covalent bonds and electronegativity:

A covalent bond is a bond that forms due to the sharing of electrons, mostly between two non-metals. If the sharing atoms are of the same type of element the electrons will be shared equally. This means the electrons will spend equal times around each atom and there will be no difference in the electronegativity between sharing atoms (the electronegativity is the measure of the strength of an atom to draw the bonding electrons towards itself). The molecules of the similar atoms are considered to be non-polar. Example, the bond between H-H in H₂ is non-polar covalent and the bond to be a pure covalent bond.

If the atoms are from different elements the electrons will spend more time around the more electronegative atom and the molecule is considered to be polar covalent

Example of polar covalent bonds is the bond between H and Cl in HCl. One electron is shared between the two atoms, this electron spend more time around the chlorine atom than around hydrogen atom.

The strength of polar covalent lies between ionic and non-covalent bonds (ionic bond, such as the bond between NaCl-metals and non-metals). For that, the bond strength of HCl (polar covalent) is stronger than between H2 (non-polar covalent) and weaker than between NaCl (ionic).

If the difference in the electronegativity between the two bonded atoms is more than 2, the bond considered to be ionic. If the difference in the electronegativity less than 2, the bond is polar-covalent. If there is no difference in the electronegativity, the bond considered to be non-polar covalent.