The coordinate covalent bond is also a special type of
covalent bond, in which both electrons forming a bond
are supplied by one atom only. The atom which supplies
the pair of electrons for bond formation is known as "Donor"
and the atom which accepts, is known as "Acceptor”.
An arrow (—>) is commonly used to denote the bond, in
which the head of an arrow pointing towards acceptor
atom. The pair of electrons possessed by donor is called
"Lone-pair" of electrons. This type of bond is
also called dative covalent bond.
In the formation of ammonium chloride, from ammonia (NH3)
and hydrogen chloride (HCl) molecules, the nitrogen (N)
atom of ammonia (NH3) acts as donor of an
electron pair and hydrogen ion (H+) of
hydrogen chloride accept it to form (NH4Cl)
Another example is provided by the formation of
hydronium ion (HO2) from water molecule and
hydrogen ion (H+), in which the oxygen atom
of water acts as donor and hydrogen ion (H+),
5.6.1 Comparison between Covalent Bond and Co-ordinate
1 The covalent bond is formed by the mutual sharing
of electrons between atoms.
2. The covalent bond is formed between the similar
or dissimilar atoms, when the electrons are mutually
3. Covalent bond may be polar or non-polar
4. Covalent bond is associated with only covalent
character because there is no electron transfer.
5. The shared pair of electrons in covalent bond are
denoted by short lines e.g. for single pair (-) for
double pair (=) and for triple pair of electrons
6. Covalent compounds are usually insoluble in
Co-ordinate Covalent bond
1. The co-ordinate covalent bond is formed by one
sided sharing of electrons.
2. Co-ordinate covalent bond is formed between two
unlike atoms, one having an electron pair available
for sharing and other must accept that electron
3. Co-ordinate covalent bond is always polar,
because it is not formed between like atoms and is
also known as co-ionic.
4. Co-ordinate covalent bond is associated with the
ionic and covalent character because of partial
transfer of electrons.
5. The shared pair of electrons in co-ordinate
covalent bond is denoted by an arrow (—>).
6. Where as co-ordinate covalent compounds are
sparingly soluble in water.