Discus of coordinate Bond

Coordinate Bond

A covalent bond results from sharing of a pair of electrons between two atoms, where atom contributes one electron to the bond. It is also possible to have an electron pair bond where both the electrons come from one of the two bonding atoms and there is no contribution from the other atom. Such bonds are called coordinate bonds or dative bonds, Coordinate bond is a special type of covalent bond in which both the bonded electron come from one of the two binding atoms. One common example is formation of ammonium ion. Even though the ammonia molecule has electronic configuration it can react with a hydrogen ion (H⁺) by donating a loan pair of electron from N atom to H⁺  ion forming the ammonium ion NH⁺₄ .

Covalent bonds are usually shown as a straight line joining the two atoms, and coordinate bonds as arrows indicating which atom is donating the electron. Similarly, ammonium donates its lone pair to boron trifluoride and by this means the boron atom attains noble gas configuration.

In a similar way a molecule of BF₃ can form a coordinate bond by accepting a loan pair from a F^- ion.

Double and Triple Bonds

Sometimes more than two electrons are shared between a pair of atoms. If four electrons are shared then there are two bonds this arrangement is called a double bond. If six electrons are shared then there are three bonds and this is called a triple bond.