Only in its pure metallic form is sodium rare. It is, otherwise, a plentiful element. 50 quadrillion tons of salt in the oceans represents most of the planet's supply.
Sodium is so chemically active that it cannot exist, for long, as a free element unless it is kept from exposure to air, water, etc. Because it is a much more active element than aluminum, it can replace it in aluminum compounds and thus free the metal.
Sodium is so chemically active that it cannot exist, for long, as a free element unless it is kept from exposure to air, water, etc.
Chlorine is a pretty nasty element in it's pure form as well.
We are actually pretty lucky to have enough sodium on this planet to keep all that chlorine out of the atmosphere.