Bonds & ions
Octet rule — অষ্টক নিয়ম
Quick answer
Atoms bond in whatever way leaves each with eight outer-shell electrons — the settled arrangement of a noble gas.
Definition
The octet rule says that atoms tend to gain, lose or share electrons until their outer shell holds eight electrons — the settled arrangement of the noble gases. Sodium hands over one electron to reach it and chlorine takes one, so satisfies both at once. Hydrogen, lithium and beryllium settle for just two electrons, and transition metals often keep bonding past a simple octet, so treat the rule as a trusty guide rather than an iron law of nature.
For example
A methane molecule shows carbon completing its octet: it shares one electron pair with each of four hydrogen atoms, reaching eight outer electrons in all.