Ionization energy The sciences of physics and chemistry use different measures of ionization energy. In physics, the unit is the amount of energy required to remove a single electron from a single atom or molecule, expressed as electronvolts. In chemistry, the unit is the amount of energy required for all of the atoms in a mole of substance to lose one electron each: molar ionization energy or enthalpy, expressed as kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol). Comparison of "E" of elements in the periodic table reveals two periodic trends: The latter trend results from the outer electron shell being
Action (physics) in time and space. Action has the dimensions of [energy]⋅[time], and its SI unit is joule-second, which is identical to the unit of angular momentum. In classical physics, the term "action" has a number of meanings. Most commonly, the term is used for a functional formula_2 which takes a function of time and (for fields) space as input and returns a scalar. In classical mechanics, the input function is the evolution q("t") of the system between two times "t" and "t", where q represents the generalized coordinates. The action formula_3 is defined as the integral of the Lagrangian "L" for