Electronegativity scale

The electronegativity measures the ability of an atom to draw electrons to itself in a chemical bond. While it is reported as an atomic property, it is concerned with bonding within a molecule. One definition of electronegativity that was proposed by Mulliken in 1934 is particularly simple, being a simple arithmetical average:

$${\rm electronegativity} \propto {1 \over 2}\left(IE_1 + EA\right)$$

The larger the electronegativity, the greater the tendency for an atom to draw electrons to itself in a chemical bond.

In general,

if $IE_1$ and $EA$ are both large, giving up an electron is unlikely, but gaining an electron is likely, and the atom tends to act as an electron acceptor, or is ``electronegative.''

if $IE_1$ is small, and $EA$ is small or negative, giving up an electron is likely, but gaining an electron is unlikely, and the atom tends to act as an electron donor, or is ``electropositive.''

Elements toward the left of the periodic table have low electron affinities, so they tend to act as electron donors, while atoms to the right of the periodic table have high electronegativities, and they tend to act as electron acceptors.