Which element has the highest electronegativity?

Fluorine is recognized as the element with the highest electronegativity due to its position in the periodic table and its atomic structure. Electronegativity is the measure of an atom's ability to attract and hold onto electrons when it is part of a compound. Fluorine, being in group 17 (the halogens), has a very high effective nuclear charge and a small atomic radius, which enables it to pull electrons towards itself more effectively than other elements.

Its electron configuration, with a single unpaired electron in its outer shell, allows it to be very eager to gain one more electron to achieve a full valence shell, reflecting a strong tendency to attract electrons. This extreme electronegativity is what makes fluorine highly reactive, particularly with alkali and alkaline earth metals. Hence, when considering electronegativity trends across the periodic table, fluorine stands out as the most electronegative element.

Chlorine and oxygen also have notable electronegativities but do not match that of fluorine. Helium, being a noble gas, does not participate in bonding in the same way, hence it is not relevant in this context of electronegativity.