The Periodic Table: Group 7 - Halogens

The Periodic Table: Group 7 - Halogens

• The elements in Group 7 of the periodic table are known as halogens.
• Halogens include the following elements: fluorine, chlorine, bromine, iodine and astatine.
• They are all non-metals that have seven electrons in their outer shell. As a result, they readily gain one electron to attain a full outer shell.
• As you move down the group, the elements become less reactive. This is because the outer shell is further from the nucleus and so the attraction for an additional electron is weaker.
• The different colours of the halogens are used to indicate their physical state. Fluorine is yellow gas, chlorine is a green gas, bromine is a red-brown liquid, and iodine is a shiny grey-black solid or violet gas.
• Halogens have low melting and boiling points, which increase down the group.
• They are poor conductors of heat and electricity.
• Halogens form both ionic salts and covalent compounds.
• They form diatomic molecules (two atoms per molecule) in their elemental state, for example, Cl2.
• The reactivity series of halogens can be demonstrated through displacement reactions. For instance, a more reactive halogen will displace a less reactive halogen from an aqueous solution of its salts.
• Halogens bond with metals easily, forming salts such as sodium chloride (common table salt).
• Chlorine is used in water treatment, bromine is used in flame retardants and iodine is necessary for making thyroid hormones in our body.
• Halogens are also used in the manufacture of organic compounds such as solvents and refrigerants.