Inter molecular forces are weak, so the molecules are not pulled very close together. More space between the molecules means that solid simple molecular compounds have low density. Weak bonds between the molecules are easily broken, so the solids are soft, and the liquids have low viscosity.
Weak inter molecular bonds are easily broken, so small covalent molecules can dissolve in similar non-polar solvents. If they have no dipole, they will not dissolve in polar solvents like water. There are no charged particles or free electrons within the simple molecules. Therefore they generally display poor thermal and electrical conductivity
Follow this sequence to determine the physical properties of any substance:
- Electronic structure
- Type of Bonding
- Type of structure
Stronger intermolecular forces (such as dipole- dipole or hydrogen bonding) are more difficult to break. Polar molecules such as water have higher melting and boiling points than non-polar molecules such as methane of similar size.