Fluorine have the highest electronegativity of all the elements because it has the largest nuclear charge and the least atomic shell, so it has the largest nuclear pull force. In other words, fluoride has the strongest ability to pull or catch an electron to form negative ion (that is, electronegativity). Bond dissociation energy of F₂  is fairly low due to the lone pair - lone pair repulsions of the two flourine atoms, which are placed so close to each other due to small size of the atom.