Question

Which of the following does not contain any co-ordinate bond?
A. $${\mathbf{H}}_3{\mathbf{O}}^{+}$$
B. $$\mathbf{B}{{\mathbf{F}}_4}^{-}$$
C. $$\mathbf{H}{{\mathbf{F}}_2}^{-}$$
D. $$\mathbf{N}{{\mathbf{H}}_4}^{+}$$

Answer 1

Hint: To find out an accurate answer to this question we should first consider understanding the co-ordinate bond. Now, coordinate bond is also known as dative bond, it is a kind of covalent bond, the only difference is that sharing of electrons is done by only one atom.

Complete answer:
Now, to identify coordinate bonds there are a few important points we need to consider. The first point is there should be a lone pair available on one atom and an empty orbital on the other one. Now in coordinate bonding the electron shares are only given by one atom, a lone pair from one atom is shared between two, to form a bond which can be shown by an arrow $(\to )$ , the arrow is put in the direction of donor to receiver.
Now by drawing the lewis structure of all four options we can find out which does not consist of a coordinate bond.
  $${\mathbf{H}}_3{\mathbf{O}}^{+}$$ : shares a lone pair with empty 1s orbital of hydrogen to form H3O+
  $$\mathbf{B}{{\mathbf{F}}_4}^{-}$$ : Fluorine shares a lone pair electron with Boron's empty 2p orbital to form a coordinate bond.
 $$\mathbf{H}{{\mathbf{F}}_2}^{-}$$ : Now there is a hydrogen bonding between H and F. So there is no formation of coordinate bond.
 $$\mathbf{N}{{\mathbf{H}}_4}^{+}$$ : coordinate bond is formed between lone pairs of nitrogen to empty 1s orbital of hydrogen.

The correct answer is option C .

Note:
We need to draw the chemical structure of a compound if we wish to find out the
coordinate bond. We try to stabilise the structure by completing all atoms octet or duplet. Now HF cannot form a coordinate bond because it makes hydrogen bonding.