How do molecular compounds bond?
Molecular or covalent compounds bond to each other by intermolecular forces of attraction.
These forces involve electrostatic attractions between the negative and positive charges in neighbouring particles.
Dipole-dipole forces are electrostatic attractions between the positive and negative ends of polar molecules.
These interactions tend to align the molecules and increase the attraction between them.
Polar molecules have a net attraction between them. Hydrogen chloride (HCl) and chloroform (CHCl₃) are examples of polar molecules.
Hydrogen bonds are an exceptionally strong type of dipole-dipole interaction. Do not confuse them with covalent bonds, such as C-H, O-H, N-H, or F-H bonds.
The simplest example of a hydrogen bond is found between water molecules.
LONDON DISPERSION FORCES
Consider the molecules of iodine. At any given instant, there may be a slightly greater electron density on one iodine atom than on the other.
This instantaneous dipole can induce a dipole in a neighbouring iodine molecule.
The induced dipole leads to an attractive force called a London Dispersion Force.
In order of decreasing strength, then, the intermolecular attractive forces among molecular compounds are
- Hydrogen bonds
- Dipole-dipole forces
- London dispersion forces