Chlorine is less reactive than fluorine because the outer electrons in a chlorine atom are further from the nucleus than the outer electrons in a fluorine atom. It is harder for a chlorine atom to gain an electron than it is for a fluorine atom.
There are three things to consider every single time relative reactivity is unknown; atomic radius, shielding, and number of electrons. The reactivity is the halogens ability to gain an electron, so number of electrons already in the atom plays a vital role. Chlorine has more electrons so repels a reacting electron with greater force than fluorine, making it less likely to react.
Fluorine also has fewer electron shells than chlorine, so there are fewer electrons between the positive nucleus and the reacting electron to essentiallly block, or weaken, the electromagnetic attraction. This is shielding. Lastly, fluorine is much smaller molecule than chlorine, and the shorter distance, or radius, between the nucleus and the electron again makes it more likely to attract the electron and react to gain a noble gas configuration.
Fluorine is the first element in the halogen group and chlorine is the second. The reactivity of the halogens decrease as we go down the group. The atomic radius increases in size with an increase of electronic energy levels.
This lowers the attraction for valency electrons of other atoms, reducing reactivity.
the molecules of each substance attract each other through dispersion (London) intermolecular force.whether a substance is solid, liquid or gas depends on the balance between the kinetic energies of the molecules and their intermolecular attractions.
