Electronegativity — তড়িৎ ঋণাত্মকতা
An atom's power to pull the shared electron pair of a bond toward itself; fluorine tops the scale at 3.98.
Definition
Electronegativity measures how strongly an atom pulls the shared electron pair in a covalent bond toward itself. On the Pauling scale fluorine is highest at 3.98, while cesium, at about 0.79, sits near the very bottom. The value rises from left to right across a period and falls from top to bottom down a group, because more protons and a smaller radius both pull harder. Big differences between bonding atoms make ionic bonds, small differences make nonpolar covalent ones.
For example
In the chlorine atom is more electronegative (3.16) than hydrogen (2.20), so the shared pair drifts toward chlorine and that end of the molecule turns slightly negative.