Considerations A chemical bond forms when it is energetically favorable, i.e., when the energy of the bonded atoms is less than the energies of the separated atoms. The ionization energy or ionization potential is the energy necessary to remove an electron from the neutral atom. It is a minimum for the alkali metals which have a single electron outside a closed shell. It generally increases across a row on the periodic maximum for the noble gases which have closed shells. The electron affinity is a measure of the energy change when an electron is added to a neutral atom to form a negative ion.
Small numbers indicate that a less stable negative ion is formed.
Groups VIA and VIIA in the periodic table have the largest electron affinities. Back Electronegativity Electronegativity is a measure of the ability of an atom in a molecule to draw bonding electrons to itself. The most commonly used scale of electronegativity is that developed by Linus Pauling in which the value 4.0 is assigned to fluorine, the most electronegative element. Lithium, at the other end of the same period on the periodic table, is assigned a value of 1. Electronegativity generally increases from left to right on the periodic table and decreases from top to bottom.