Question

what is the increasing strength of hydrogen bonding?
$\text{ }\left( X.....H-X \right)\text{ }\left( X=\text{ O , S ,F, Cl , N} \right)\text{ }$ ?
A) $\text{ S }<\text{ Cl }<\text{ O }<\text{ N }<\text{ F }$
B) $\text{ S }<\text{ N }<\text{ Cl }<\text{ O }<\text{ F }$
C) $\text{ S }<\text{ Cl }<\text{ N }<\text{ O }<\text{ F }$
D) None of these

Answer 1

Hint: Hydrogen bond is a strong intramolecular force of attraction between the hydrogen atom and the electronegative atom such as N, O, F, S,$\text{ Cl }$ etc. The strength of the hydrogen bond is directly related to the electronegativity difference between the hydrogen and electronegative atom. Greater the difference is the strength of the hydrogen bond.

Complete Solution :
- Hydrogen bonding is considered a special type of attraction between the molecules.it is observed because of the force of attraction between the hydrogen and the highly electronegative atoms such as N, O, or F atoms. Hydrogen bonds are strong bonds and their bond strength lies in the range of $\text{ 4kJ }$ to $\text{ 50kJ }$ .
- The strength of hydrogen bond as $\text{ N}-\text{H }$ , $\text{ O}-\text{H }$ or $\text{ F}-\text{H }$depends on the electronegativity difference between the hydrogen and the electronegativity atom. The electronegativities difference of the atoms exhibiting hydrogen bonds is as shown below:

Element	Electronegativity value
$\text{ H }$	$\text{ 2}\text{.1 }$
$\text{ S }$	$\text{ 2}\text{.58 }$
$\text{ N }$	$\text{ 3}\text{.0 }$
$\text{ Cl }$	$\text{ 3}\text{.16 }$
$\text{ O }$	$\text{ 3}\text{.5 }$
$\text{ F }$	$\text{ 4}\text{.1 }$

The difference in the electronegativity of the atom, hydrogen atom bears a large amount of partial positive charge while the N, O, F, S, etc. have a large partially negative charge. The strength of hydrogen bonds is of very much importance.
- The strength of the hydrogen bond between the hydrogen and electronegative atoms is directly related to the electronegativity difference between the atoms forming a hydrogen bond.
- More difference in the electronegativities between hydrogen and the O, N, or F atom results in the increase in the polarity of a covalent bond.
- The difference in the electronegativities of various hydrogen bond are listed as below:

Hydrogen bond	Electronegativity value
$\text{ S}-\text{H }$	$\text{ 0}\text{.48 }$
$\text{ N}-\text{H }$	$\text{ 0}\text{.9 }$
$\text{ Cl}-\text{H }$	$\text{ 1}\text{.06 }$
$\text{ O}-\text{H }$	$\text{ 3}\text{.40 }$
$\text{ F}-\text{H }$	$\text{ 2}\text{.0 }$

- It is clear that , the hydrogen bond formed between the H and fluorine $\text{ F}-\text{H }$ has a greater electronegativity difference and $\text{ S}-\text{H }$ bond has a lowest electronegativity difference .Thus $\text{ F}-\text{H }$ bond has a higher bond strength followed by the $\text{ O}-\text{H }$, $\text{ Cl}-\text{H }$, $\text{ N}-\text{H }$ and $\text{ S}-\text{H }$.The order of increasing strength of hydrogen bonding is given as,
$\text{ S }<\text{ N }<\text{ Cl }<\text{ O }<\text{ F }$
So, the correct answer is “Option C”.

Note: Note that hydrogen bonds have great significance in the biological system. It is responsible for holding DNA or the protein molecules together. The hydrogen bonding between the base pairs may give a characteristic helical structure to DNA.