Illustrated Glossary of Organic Chemistry

Covalent bond: A chemical bond formed by the overlap of atomic orbitals. The electron pair between the atoms is shared to some extent. A bond is considered to be covalent when the electronegativity difference between the bonded atoms is 1.7 or less.


Electronegativity difference = 0; a covalent bond.


Electronegativity difference = 0.7;  a polar covalent bond.


Electronegativity difference = 1.9; an ionic bond.