What are Halogens? (Group 17 Elements)

Halogens are a group of highly reactive non-metal elements located in Group 17 of the periodic table.

• The word 'Halogen' comes from Greek words: 'Hal' meaning Salt, and 'gen' meaning to produce/form.
• Therefore, Halogen literally means "Salt Formers". When these elements react with metals, they produce salts (e.g., Sodium + Chlorine = Sodium Chloride / Table Salt).

There are five main elements in the Halogen group:

1. Fluorine (F): A pale yellow, highly toxic gas. It is the most reactive element on the entire periodic table!
2. Chlorine (Cl): A greenish-yellow gas used in bleach and swimming pools to kill bacteria.
3. Bromine (Br): A dark red, fuming liquid. (It is the only non-metal that is a liquid at room temperature).
4. Iodine (I): A dark purple/black solid that sublimates into a purple gas. Essential for human thyroid health.
5. Astatine (At): A highly radioactive and extremely rare element.

• Valence Electrons: All halogens have exactly 7 electrons in their outermost shell.
• High Electronegativity: Because they are just one electron short of a perfect 'Octet' (8 electrons), they aggressively steal electrons from other elements to become stable.
• Diatomic Molecules: In nature, pure halogens are never found as single atoms. They always pair up with themselves (e.g., F₂, Cl₂, Br₂, I₂).