Question

Define a coordinate bond and give the conditions for its formation.

Answer 1

the bond formed between 2 atoms by sharing a pair of electrons, provided entirely by one of the combining atoms but shared by both is called a coordinate bond or dative bond, e,.g., ammonium ion, hydronium ion
conditions for the formation of coordinate bond
1) one of the 2 atoms must have at least one lone pair of electrons e. g, ammonia, water
2) another atom should be short of at least a lone pair of electrons, e. g., hydrogen ion

Answer 2

Let's take the example of BF3 and NH3.
BF3 is an electron deficient compound because it has only 6elctrons around it .It needs 2more to satisfy it's octet.Now NH3 is an electron rich compound as Nitrogen has a lone pair of electrons on it . Now THIS lone pair of electrons can be donated to BF3 to satisfy is octet. This bond formed is called a coordinate covalent bond (IT is denoted by an arrow)

NH3 +BF3. =. NH3--->BF3