The element with the highest electronegativity is fluorine (F). Fluorine has an electronegativity value of 3.98 on the Pauling scale, which is the highest among all the elements.
Electronegativity is a measure of an atom's ability to attract electrons towards itself when it forms a chemical bond with another atom. Fluorine has the highest electronegativity because it has a small atomic radius and a high effective nuclear charge.
Even though fluorine has a lower atomic number than some other elements, such as chlorine (Cl) or bromine (Br), which have higher atomic numbers, it has a higher electronegativity due to its atomic structure. Fluorine has a smaller atomic radius, meaning its outermost electrons are closer to the nucleus and experience a stronger attractive force from the positively charged protons in the nucleus. Additionally, fluorine has a high effective nuclear charge because its outermost electron is shielded by only a few inner electrons, resulting in a stronger attraction for electrons.
These factors contribute to fluorine's high electronegativity, making it the element with the highest electronegativity on the periodic table.