The element with the highest electronegativity is fluorine, according to the Pauling electronegativity scale. Linus Pauling first gave fluorine an arbitrary electronegativity reading of 4.0, and then he assigned the other elements smaller numbers on the scale based on how their electronegativities measured up to fluorine's.
Electronegativity is a measure of how tightly an atom holds on to its electrons. Fluorine, with seven electrons in its outermost energy level, has a high affinity for its electrons. It holds onto its existing electrons securely and also wants to collect another electron from other elements. The electronegativity of elements on the periodic table increases from bottom to top and from left to right. Fluorine lies at the top right of the table and has the highest electronegativity.