Chapter 14, Problem 4A

Interpretation Introduction

Interpretation: The reason for boiling point of water to be greater than $H_{2}S$ , $H_{2}Se$ and $H_{2}Te$ needs to be explained with the help of hydrogen bonding.

Concept introduction: The hydrogen bond may be defined as a strong dipole-dipole forces of attraction that operates between a hydrogen atom that is covalently bonded to an atom of high electronegativity.

Answer to Problem 4A

Due to hydrogen bonding in water its boiling point is greater than $H_{2}S$ , $H_{2}Se$ and $H_{2}Te$ .

Explanation of Solution

The covalent bond between a hydrogen and an electronegative oxygen is considerably polar because the electronegative atom attracts the bonding electron towards itself. The partial positive charge on hydrogen attracts the partial negative charge of an electronegative oxygen forming what is called hydrogen bonding.

  $H_{2}O$ molecules can have dipole-dipole force of attraction as well as hydrogen bonding as an intermolecular force. Hence extra amount of energy is needed to dissociate two $H_{2}O$ molecules. On the other hand $H_{2}S$ , $H_{2}Se$ and $H_{2}Te$ can form only dipole-dipole force but not hydrogen bonding and hence their boiling point is lower than $H_{2}O$ .

Conclusion

Due to hydrogen bonding in water its boiling point is greater than $H_{2}S$ , $H_{2}Se$ and $H_{2}Te$ .