The most used definition of electronegativity is that an
element's electronegativity is the power of an atom when in a
molecule to attract electron density to itself. The
electronegativity depends upon a number of factors and in
particuler as the other atoms in the molecule. The first scale
of electronegativity was developed by Linus Pauling and on his
scale iodine has a value of 2.66 on a scale running from from
about 0.7 (an estimate for francium) to 2.20 (for hydrogen) to
3.98 (fluorine). Electronegativity has no units but "Pauling
units" are often used when indicating values mapped on to the
Pauling scale. On the interactive plot below you may find the
"Ball chart" and "Shaded table" styles most useful. There are a
number of ways to produce a set of numbers representing
electronegativity and five are given in the table above. The
Pauling scale is perhaps the most famous and suffices for many
purposes. WebElements now has a WebElements shop at which you
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