Chapter 9, Problem 55QRT

Interpretation Introduction

Interpretation:

The reason behind relatively higher boiling point of water has to be explained.

Concept Introduction:

London forces:

London(dispersion) forces happen because sometimes, when adjacent molecules line up so that they form temporary dipoles, there is a weak force of attraction between the end of one molecule where more of the electrons are accumulating at the moment and the end of a second molecule where the electrons are not staying at the moment.  London(dispersion) forces are present between molecules of all molecular substances.

Hydrogen bonding:

Hydrogen bonding is a special form of dipole-dipole interaction.  When a hydrogen atom is bonded to a small, electronegative atom (like $N,OandF$), then the electronegative atom pulls electron density away from the hydrogen atom.  This results a partial positive charge on the hydrogen atom and a partial negative charge on the electronegative atom.  The hydrogen atom on one molecule will be attracted to the electronegative atom on another molecule.  Like this hydrogen bonding takes place.

Dipole-dipole Interaction:

This kind of attraction occurs between permanent dipoles in adjacent polar molecules or between two polar groups in the same large molecule.  Molecules having permanent dipoles attract each other when the partial positive region of one is close to the partial negative region of another.