Inter molecular bonding
Between the molecules.

Intermolecular bonding of polar molecules  such as  HF.

The image above shows a polar molecule (HF) and the way the poles of each molecule interact to bring about intermolecular bonding called dipole-dipole bonding..

Uneven sharing of electrons in a covalent bond is one of the factors that gives rise to polar molecules. The other factor is a lack of symmetry in the molecule, but we will discuss this a little later. A polar molecule is one that has small charges (not single charges as in ionic bonding) on opposite ends. Polar molecules attract each other via the charges on each end. Attraction of opposite ends of polar molecules is called dipole-dipole bonding. This form of intermolecular bonding is extremely weak when compared to ionic or metallic bonding. However, it is strong enough to allow water to exist as a liquid at room temperature. This strong form of dipole-dipole bonding is given a special name, hydrogen bonding.

Notice the animation on the right of HF undergoing dipole-dipole bonding. Note how the opposite ends of the molecules align themselves so that the small negative and positive charges attract.


The animation on the left shows water molecules aligning themselves during dipole-dipole bonding. Because of this alignment, which comes about due to strong dipole-dipole attraction called hydrogen bonding, large gaps are created between the molecules. For this reason alone water expands when it is cooled and causes bottles of liquid to explode when placed in the freezer.
Dipole-dipole bonding is at the weaker end of the bonding spectrum when compared to ionic, metallic and 3D covalent bonding. With this in mind we have a strong form of dipole-dipole bonding that we have just discovered to be hydrogen bonding. There is also a weaker form of dipole-dipole bonding that exists between all molecules whether they are polar (have permanent dipoles) or not, known as dispersion forces.
The posititve charge on the hydrogen atom The electrons being shared are attracted closer to the oxygen atom. The negative charge on the oxygen atom The positive charge on the hydrogen atom Attraction of the of the permanent dipoles of each molecule.