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### Theory:

Coordinate Covalent bond or Dative bond:

In the formation of a normal covalent bond, each of the two bonded atoms contributes one electron to construct the bond.
A covalent bond is formed between two atoms by sharing two electrons, both of which come from combining atoms. This type of bond is known as a Coordinate covalent bond or a Dative bond.
• The lone pair of electrons from an atom in a molecule is usually involved in dative bonding.
• The atom that provides the electron pair is known as the donor atom, while the atom that accepts the electron pair is known as the acceptor atom.
• An arrow ($\to$) leading from the donor to the acceptor atom represents a coordinate covalent bond.
Formation of coordinate covalent bond:

Consider two atoms, $$A$$ and $$B$$. Assume that atom $$A$$ has an unshared lone pair of electrons and atom $$B$$ lacks two electrons in its valence shell.

Atom $$A$$ now donates its lone pair, accepted by atom $$B$$.

Thus, the lone pair of electrons formerly belonged to atom A is now given by both the atoms, and the bond made by this mutual sharing is called a Coordinate covalent bond $$A$$ $\to$ $$B$$.

Coordinate covalent bond formation
Example:
($$NH_4{^+}$$, $$NH_3$$ $\to$ $$BF_3$$)
Illustration 1- Formation of a coordinate covalent bond between $$NH_3$$ $$BF_3$$ molecules:
• The donated pair of electrons arrive from an already made molecule to another acceptor molecule.
• In this case, the molecule ammonia ($$NH_3$$) contributes a single pair of electrons to the electron-deficient molecule boron trifluoride ($$BF_3$$).
• Thus, $$NH_3$$ (donor molecule) and $$BF_3$$ (acceptor molecule) form a coordinate covalent bond, which represent $$NH_3$$  $$BF_3$$.
Example of coordinate covalent bond