Why do induced dipole-induced dipole forces increase as the number of electrons in a molecule increases?

a. More electrons make the electron cloud more polarizable.

b. More electrons means that there are more protons in the nuclei which hold the electrons more tightly and polarize them.

c. Molecules with more electrons are more likely to be held together by ionic bonds.

I wouldn't pick any of them; I would have preferred that one choice be because the electron cloud is larger which makes the atom more polarizable; however, a comes the closest.

The correct answer is a. More electrons make the electron cloud more polarizable.

To understand why induced dipole-induced dipole forces increase with the number of electrons in a molecule, we need to consider how these forces arise. Induced dipole-induced dipole forces, also known as London dispersion forces, result from temporary fluctuations in electron distribution within molecules.

When two non-polar molecules approach each other, the electron cloud of one molecule can induce a temporary dipole in the other molecule by repelling the electrons, causing a slight shift in electron density. This induced dipole then induces an opposite dipole in the first molecule. These temporary dipoles create attractive forces between the molecules, known as London dispersion forces.

Now, as the number of electrons in a molecule increases, the electron cloud becomes more extensive. This increased electron cloud leads to a higher polarizability of the molecule. Polarizability refers to how easily the electron cloud can be distorted or polarized by an external electric field.

When a molecule has more electrons, there is a greater number of electrons available to be shifted or distorted by an external electric field. As a result, the electron cloud becomes more easily polarized, and the magnitude of induced dipoles increases.

Therefore, option a is correct. More electrons in a molecule make the electron cloud more polarizable, leading to stronger induced dipole-induced dipole forces or London dispersion forces.