Defining Halogens
Halogens are a group of five non-metallic elements found in Group 17 (or VIIA) of the periodic table: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The term 'halogen' means 'salt-forming' from Greek, reflecting their tendency to form salts when reacting with metals. They are highly reactive due to their electron configuration, seeking one additional electron to complete their outer shell.
Key Properties and Characteristics
A defining characteristic of halogens is their high electronegativity, meaning they strongly attract electrons. They all exist as diatomic molecules (e.g., F₂, Cl₂) in their elemental form. As you move down Group 17, their melting and boiling points increase, and their physical state at room temperature changes from gas (F, Cl) to liquid (Br) to solid (I, At). They are toxic and corrosive in their pure form.
Common Examples and Applications
Chlorine (Cl) is widely known for its use as a disinfectant in water treatment and swimming pools, and in the production of PVC. Fluorine (F) is essential for producing fluorocarbons and is added to toothpaste and water to prevent tooth decay. Iodine (I) is vital for thyroid function in humans and is used as an antiseptic. Bromine (Br) finds use in flame retardants and photographic films.
Why Halogens Are So Reactive
Halogens are among the most reactive nonmetals because they have seven valence electrons and readily gain a single electron to achieve a stable octet configuration, similar to noble gases. This strong desire to gain an electron drives their reactions with many other elements, especially alkali metals and alkaline earth metals, forming ionic compounds (salts) through vigorous reactions.