CBSE Class 11-science Answered

A co-ordinate bond (also called a dative covalent bond) is a covalent bond (a shared pair of electrons) in which both electrons come from the same atom.

Example:

In the formation of ammonium chloride, ammonium ion is formed by the attachment of hydrogen atom from hydrogen chloride to ammonia molecule through co-ordinate bonding. This is called co-ordinate or dative bond because, only the nucleus of hydrogen atom of hydrogen chloride is transferred to ammonia molecule leaving electron of hydrogen with chlorine atom forming negative charge on chlorine atom. Hydrogen atom uses lone pair of electrons of nitrogen for the attachment which is shared between nitrogen and hydrogen.

Hydrogen bonds:

The delta + hydrogen atom is so strongly attracted to the lone pairs of electrons on oxygen atom of water that it is almost like beginning of formation of co-ordinate bond. But it doesn’t go that far. Still the attraction is stronger than dipole-dipole attraction.