chemistry-instantaneous dipoles in pure covalent molecules

Instantaneous dipoles in other symmetrical molecules
Symmetrical molecules such as O₂, N₂, Cl₂, F₂ and H₂ have pure-covalent intermolecular bonding. Electrons are shared evenly so the molecule has no permanent dipole. Lets look at a simple hydrogen molecule. Look at the animation on the right and you will see the electrons shared evenly.
But sometimes the random nature of the electron's movement may cause an uneven distribution of electrons inside the molecule. This leads to the molecule becoming polar for an instant. Once again dispersion forces act between the molecules.
Since dispersion forces depend on random movement of electrons it makes sense to assume that the more electrons present in the molecule the greater the chance of the formation of instantaneous dipoles. The greater the frequency of instantaneous dipole formation the greater the strength of the dispersion forces. Since melting temperature is an indication of intermolecular bonding strength, place the following molecules in order of increasing melting temperature. N₂, Cl₂, F₂, O₂, I₂and H₂ Solution Why is CCl₄ a liquid at room temperature but I₂is a solid? Solution Click to hide solution Since all the molecules rely on dispersion forces only for intermolecular bonding the size of the molecule is important. The geater the molecule the greater the force of attraction and therefore the higher the melting temperature. H₂> N₂> O₂> F₂ > Cl₂> I₂ Click to hide solution I₂ is a bigger molecule than CCl₄ . I₂ has 104 electrons but CCl₄ has 74 electrons.