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

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.