Physical Properties of Halogens
Boiling points increase as you go down the group.
Halogens exist as non-polar diatomic molecules held together by induced dipole-dipole interactions (London forces).
As you go down the group, the molecules become larger with more electrons. This causes the induced dipoles to become stronger, meaning more energy is required to overcome the forces between molecules.
Minimum: -1
Maximum: 0
Minimum: -1
Maximum: +7
Fluorine is the most electronegative element in the periodic table. It can only attract electrons to form a -1 state (or share them with itself for 0). No other element is strong enough to remove electrons from fluorine.
Chlorine is less electronegative than elements like Oxygen or Fluorine. Chlorine has 7 valence electrons, and when it bonds with a more electronegative element (like in ClO4–), it can form bonds using all 7 electrons, resulting in a maximum oxidation state of +7.
The electron affinity gets less exothermic (less negative) as you go down the group (from Chlorine downwards).
As you go down the group, the atomic radius increases and the amount of shielding increases. These factors outweigh the increase in nuclear charge, resulting in a weaker electrostatic attraction between the nucleus and the incoming electron being gained.
The bond strength decreases as you go down the group (from Cl-Cl to I-I).
As the atoms get larger, the bond length increases. This results in a weaker attraction between the two nuclei and the shared pair of electrons, making the bond easier to break.