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Nonpolar molecules generally have an equal distribution of electrons, and therefore charge, due to their symmetry about the origin which results in limited interactions between nonpolar molecules. The primary interactions between nonpolar molecules are London Disperson forces.
The interactions between nonpolar molecules are limited to the weakest of intermolecular forces, London Dispersion Interactions, due to the symmetry of the polar bonds of the molecules that result in an even sharing of electrons between different atoms. These London dispersion forces stem from the instantaneous dipoles that occur from random, momentary shifts in charge caused by the constant movement of electrons. The instantaneous dipoles allow the attraction between two nonpolar molecules as a positive instantaneous dipole from one molecule is attracted to an induced negative instantaneous dipole of a second molecule (See Figure 1).
Figure 1: Random movement of electrons create an instantaneous dipole that results in a momentary attraction between two nonpolar molecules. Source: Original work.
Nonpolar molecules are symmetrical about the center of the molecule. This is to balance the electronegativity of the molecule, as each charge around the central atom must balance in order for there to be no overall polarity to one side of the molecule.
The bonds in nonpolar molecules are typically covalent, promoting an even sharing and distribution of electrons within a molecule which results in a nonpolar molecule.
Consequent Effects of London Dispersion Forces
The weak intermolecular forces allow nonpolar molecules to:
1. Is an organic molecule always a nonpolar molecule?
2. Do intermolecular forces between nonpolar molecules increase or decrease as the size of the molecules become bigger? Why or why not?
3. What kind of forces are present between nonpolar molecules?
4. Why are most noble gases diatomic if their electron shells are already filled?
5. The electronegativity values of molecule A are very similar and the electronegativity values of molecule B differ greatly. Which molecule most likely interacts primarily via instantaneous dipole-induced dipole moments with another molecule of the same type? Why?
This material is based upon work supported by the National Science Foundation under Grant Number 1246120