Electronegativity, as described by L. Pauling, is “the power of an atom in a molecule to attract electrons to itself.” The concept of electronegativity can be traced to 1811 when J. J. Berzelius proposed an electrochemical basis for chemical affinity and classified various elements as being either electropositive or electronegative. With the concept of electronegativity, a vast number of observations of chemical and physical properties have been either correlated or predicted. Quantitative definitions and scales of electronegativity have been based not on electron distribution itself, but on properties that were assumed to reflect electronegativity.