Question

why do atoms combine to form molecules

Answer 1

The atoms of only a few elements called noble gases (such as Helium, neon, Argon, Krypton, etc. ) are chemically unreactive and exist in the free state as single atoms.
Atoms of most of the elements are chemically very reactive and do not exist in the free state as single atoms.

Therefore, they usually exist in 2 ways :-

1) in the form of molecules, and
2) in the form of ions .

Hope it helps u ^_^

Answer 2

→Atoms form chemical bonds with other atoms when there's an electrostatic attraction between them. This attraction results from the properties and characteristics of the atoms' outermost electrons, which are known as valence electrons.