What is a coordinate covalent bond?
A donor bond, in which the two electrons forming the bond formally derive from the ONE atom...............
And it is observed in acid-base chemistry, and in coordination chemistry:
Ammonia is a fairly weak base, and it is conceived to undergo reaction with water to give ammonium ion, and hydroxide ions.........
Coordination chemistry, the chemistry of transition metal chemistry with various ligand donors is replete with coordinate bonds. Why?