Question

What is "stability of atoms"?

Answer 1

The number of electrons on the outer shell determines how reactive or stable that atom is.If the outer shell is filled, the atom is stable. Atoms with unfilled outer shells are unstable, and will usually form chemical bonds with other atoms to achieve stability. Example of an unstable atom with a single electron in its outer-most shell. Example of an unstable atom with 7 electrons in its outer-most shell.
The unstable atoms are more reactive.