Properties of Halogens

Study Notes

Fluorine and chlorine are in the gaseous state, bromine is in the liquid state, and iodine is in the solid state.

The melting and boiling points of halogens increase with an increase in the atomic number of the element.
All halogens are colored due to the absorption of radiation in the visible region, resulting in the excitation of electrons in the outer shell to higher energy levels.
Halogens exhibit a -1 oxidation state, but chlorine, bromine, and iodine can also exhibit +1, +3, +5, and +7 states in combination with highly electronegative atoms of fluorine and oxygen.
Halogens are highly reactive in nature and often react with metals and non-metals to form halides.

The reactivity of the halogen family decreases down the group.
Halogens readily accept electrons as they are short of one electron to form an octet, hence, they have a strong oxidizing nature.
Fluorine is the strongest oxidizing agent in the halogen family.

Interhalogen compounds are formed when halogen-group elements react with each other.
The general formula of most interhalogen compounds is XYn, where n = 1, 3, 5, or 7, and X is the less electronegative of the two halogens.
There are never more than two types of halogen atoms in an interhalogen molecule.
Interhalogen compounds are of four general types: AX, AX3, AX5, and AX7.

Interhalogen compounds are prone to hydrolysis and ionize to give rise to polyatomic ions.
Interhalogens are generally more reactive than halogens, except for fluorine.
This is because A-X bonds in interhalogens are weaker than the X-X bonds in dihalogen molecules.

Chlorine monofluoride is a volatile interhalogen compound with the chemical formula ClF.
It is a colorless gas at room temperature and is stable even at high temperatures.
When cooled to -100°C, ClF condenses as a pale yellow liquid.

The hydrogen halides are colorless gases at standard conditions for temperature and pressure (STP), except for hydrogen fluoride, which boils at 19°C.
Hydrogen fluoride exhibits hydrogen bonding between molecules, resulting in the highest melting and boiling points of the HX series.

Pseudohalogens are polyatomic analogues of halogens, whose chemistry resembles that of the true halogens, allowing them to substitute for halogens in several classes of chemical compounds.
Pseudohalogens occur in pseudohalogen molecules, inorganic molecules of the general forms Ps–Ps or Ps–X (where Ps is a pseudohalogen group), such as cyanogen; pseudohalide anions, such as cyanide ion; inorganic acids, such as hydrogen cyanide; as ligands in coordination complexes, such as ferricyanide; and as functional groups in organic molecules, such as the nitrile group.
Well-known pseudohalogen functional groups include cyanide, cyanate, thiocyanate, and azide.