Atoms & structure
Valence electron — যোজ্য ইলেকট্রন
Quick answer
Valence electrons are the electrons in an atom's outermost shell — the ones that actually form bonds.
Definition
Valence electrons occupy the outermost shell of an atom, and they alone take part in bonding and reactions. For main-group elements the count follows the group: Group 1 metals have one, Group 2 have two, Group 17 have seven, and Group 18 noble gases have full shells. Atoms tend toward a full outer shell of eight — the octet rule — by sharing, gaining or losing valence electrons. Count them right and you can predict formulas, valency and reactivity before your teacher finishes the sentence.
For example
Sodium (2, 8, 1) hands its single valence electron to chlorine (2, 8, 7), and the pair settles as the salt you sprinkle on your dal.