Question

2) why
do
some elements exist as molecules&
some as atoms​

Answer 1

Answer:

An element like helium, neon, argon etc. already have this octet of electrons, so they are stable as they are. So, they don't combine with other atoms; so these elements (inert gases) exist as atoms. ... These diatomic molecules have the octet structure and are stable.

Explanation:

Answer 2

Answer:

An element like helium, neon, argon etc. already have this octet of electrons, so they are stable as they are. So, they don't combine with other atoms; so these elements (inert gases) exist as atoms. ... These diatomic molecules have the octet structure and are stable.