Group 7 Elements - The Halogens

The Halogens are the elements in Group 7 of the periodic table.
They include: fluorine, chlorine, bromine, iodine, and astatine.
These elements are all non-metals with seven valence electrons, allowing them to readily gain one electron to achieve a stable octet.
They are very reactive; reactivity decreases down the group from fluorine to astatine.
They exist as diatomic molecules (F2, Cl2, Br2, I2, and At2) in their elemental form.
The halogens show trends in physical and chemical properties.

Physical Properties

State at Room Temperature: Fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids.
Colour: Fluorine is very pale yellow, chlorine is yellow-green, bromine is red-brown, iodine is violet-black, and astatine’s colour is not well established due to its rarity and high radioactivity.
Melting and Boiling Points: These increase down the group due to increases in intermolecular forces.

Reactivity: Halogens are very reactive due to their desire to gain an electron to achieve a stable electron configuration. Their reactivity decreases down the group due to increasing atomic size and decreasing effective nuclear charge.
Formation of Salts: Halogens can displace less reactive halogens from their salts in solution, known as a displacement reaction.

Fluorine: Used in toothpaste for prevention of dental cavities.
Chlorine: Used for water purification and in the manufacturing of PVC.
Bromine: Used in photographic film and fire retardants.
Iodine: Used as an antiseptic and in the production of thyroid hormones.
Astatine: This radioactive element is used in cancer treatment, although its use is very limited due to its rarity and short half-life.