A coordinate (dative) bond forms when both electrons in the shared pair come from one atom (the donor). The resulting bond is identical to a normal covalent bond once formed — it differs only in origin. Examples: NH4+ (N donates its lone pair to H+), H3O+ (O donates to H+), BF3.NH3 (N donates to empty p-orbital of B). Back bonding is a special type of pi-coordinate bond where a filled p-orbital on one atom overlaps with an empty orbital on an adjacent atom. In BF3, fluorine's filled 2p orbital overlaps with boron's empty 2p orbital, giving partial double bond character. This makes B-F bond shorter than expected and explains why BF3 is a weaker Lewis acid than BCl3 (less effective back bonding with larger Cl).