Question

State the reason why atoms cannot exist independently and molecules can?

Answer 1

most atoms of elements do not have octet and they try to attain noble gas configuration , that's why they react and form bonds and cannot exist independently whereas molecules are group of atoms that have form bonds

Answer 2

Molecules are the smallest independent particle of a matter.

But on the other hand atoms are not independent molecule because they are not always octet, they often build ions ,positive or negative, which are not stable in real circumstances which.

For that excess amount of energy of an atom cannot be a independent particle.

(Exception:Atoms of Noble Gases)