Chapter 18, Problem 1TC

Rank the following bonds in order of increasing polarity:

(a) $\text{C}-\text{H}$

(b) $\text{O}-\text{H}$

(c) $\text{N}-\text{H}$

To determine

The ranking of following bonds in order of increasing polarity:

(a) $\text{C}-\text{H}$

(b) $\text{N}-\text{H}$

(c) $\text{O}-\text{H}$

Answer to Problem 1TC

The ranking of bonds in order of increasing polarity: $\text{C}-\text{H}<\text{N}-\text{H}<\text{O}-\text{H}$.

Explanation of Solution

A polar bond is formed through sharing of electrons mutually between two different atoms having a slight electro negativity difference between them. In a polar bond, the atom with slightly higher electro negativity gains a negative charge while the atom with slightly lower electro negativity gains a positive charge.

Here in the given polar covalent bonds: $\text{C}-\text{H,N}-\text{H},\text{O}-\text{H}$, the hydrogen will have a slight positive charge while C, N, and O atoms will have a slight negative charge are they are more electronegative than the hydrogen.

Since we know the electro negativity of an atoms gets increased while moving across the period and due to which the polarity of the bond of different atoms with hydrogen also increases. Thus, according to this among C, N and O atoms, the carbon atom is least electronegative, the nitrogen atom is slightly more electro negative than carbon and the oxygen atom is largely electro negative. Thus, the polarity of bonds also increases with increase in electro negativity, that is, the $\text{C}-\text{H}$ is least polar, then $\text{N}-\text{H}$ bond and the $\text{O}-\text{H}$ is highly polar.

Thus, the increasing order of polarity of given bonds are as follows; $\text{C}-\text{H}<\text{N}-\text{H}<\text{O}-\text{H}$.

Conclusion:

Therefore, the ranking of bonds in order of increasing polarity: $\text{C}-\text{H}<\text{N}-\text{H}<\text{O}-\text{H}$.