Why is the electron affinity for clorine is greater than the electron affinity for iodine?

Answer 1

Generally electron affinity goes up as you go from left to right across the Periodic Table, and decreases as you go down a column. However, fluorine is an exception -- and the element with the highest electron affinity is chlorine.

(Note that the most electronegative element is fluorine however; 'electronegativity' is not exactly the same as 'electron affinity'.)

Electronegativity is the ability of an atom in a molecule to draw bonding electrons to itself

Electron affinity is a measure of the energy change when an electron is added to a neutral atom to form a negative ion.

The reason that the electron affinity is not as high as might otherwise be predicted for fluorine, is that it is an extremely small atom, and so it's electron density is very high. Adding an additional electron is therefore not quite as favorable as for an element like chlorine where the electron density is slightly lower (due to electron-electron repulsion between the added electron and the other electrons in the electron cloud).

Answer 2

The irregularity in the electron affinity trend between Cl and F is due to the small size of the F atom. Although F definitely has a higher attraction for an electron than Cl (as evidenced by its high electronegativity value), the small size of the F atom means that adding an electron creates significant repulsion. Since electron affinity is an energy measurement, the total energy associated with electron affinity winds up being the energy that is released by the electron binding to the nucleus, minus the energy involved in overcoming the electrical repulsion in the outer shell.

By the way, you might notice that when you look at atomic radius Ne is slightly larger than F, another irregularity in the trend which is caused by needing more room for the eight electrons in the valence shell relative to seven in F.

Answer 3

Cholrine is more reactive than bromine because it is higher on the table. It has a greater electronegativity, (the thing that pulls electrons toward an atom) and so it will bond with more things. More bonds more reactions. Higher reactivity

Answer 4

Cl has less shielding, therefore more attraction for its valence electrons, so it's easier to gain electrons. The ease to gain electrons indicates that Cl has a higher electron affinity.

Answer 5

As you move down in a group, electron affinity decreases, or becomes less negative. This occurs because it is further away from the nucleus and is less likely to accept an electron.