Question

why is fluorine more electronegative than chlorine,bromine and iodine?

Answer 1

All the elements you have mentioned belong to Group 17( The Halogens). In any Group the electronegativity of the elements decrease downward. Electronegativity is the ability of an element to attract the bonded electrons towards itself. Atomic size plays a part in this as closer the electrons are to the nucleus of an atom the attraction between them increases. Thus increase in size leads to less attraction of electrons by the same nucleus. Accordingly the order of electronegativity of the given elements would be: Fluorine > Chlorine > Bromine > Iodine. ( Fluorine has the highest electronegativity.)