Ionization energy — আয়নীকরণ শক্তি
Ionization energy is the energy needed to pull the outermost electron off a gaseous atom.
Definition
Ionization energy (IE) is the energy needed to pluck one electron from an isolated gaseous atom — the atom's grip on its outermost electron — reported in kJ per mole. The pattern mirrors atomic radius in reverse: IE climbs across a period as nuclear charge tightens, and falls down a group as shells swell and the outer electron drifts farther from the pull. Noble gases top their periods — helium needs about 2,372 kJ/mol — while alkali metals sit at the bottom, letting go easily to form +1 ions.
For example
Sodium's first ionization energy is a low 496 kJ/mol, so it surrenders its outer electron readily — that ease is what makes it a metal, a +1 ion former, and a vigorous guest in water.