They are very reactivenonmetals, neverfoundfree in nature because of their reactivity, and are foundascompounds with metals (salts)
Halogens
They are all toxic or harmful because they are so reactive
Before antiseptics, iodine was used to clean wounds as it is harmful to all things, including bacteria
Electron structure of halogens
All halogens have seven electrons in their outer shell, and can easily obtain a full outer shell by gaining one electron
Halogens all gain an electron in reactions to form negative ions with a -1 charge
How do halogen molecules exist?
Each atom can achieve a full outer shell by sharing one electron with another atom to form a single covalent bond, so all halogens exist as diatomic molecules
General properties of the halogens
Poisonous and smelly
Brittle and crumbly when solid
They become darker in colour down the group
Halogens are non-metals and so do not conduct electricity
Physical state of the halogens
The melting and boiling points of the halogens increase down the group, as the molecules become bigger. Astatine is a solid at room temperature.
Halogen vapours
Bromine and iodine have low boiling points, so they produce vapour at relatively low temperature. Iodine can change directly from a solid to a gas without becoming a liquid, which is called sublimation.
How do the halogens react with metals?
Halogens readily react with most metals to form ionic compounds called metal halides, as halogens need to gain electrons and metals need to lose electrons.
Halides
When halogens react, they become negative ions by gaining an extra electron, and the name of the halogen changes to end in '-ide' instead of '-ine'.
The reactivity of the halogens decreases as you go down the group.
Equations of halogens and iron
Halogen + iron → iron (III) halide
Electron structure affects reactivity
The reactivity of the halogens decreases going down group 7 because the atoms get larger, the outer shell is further from the nucleus and shielded by more electron shells, making it harder to attract another electron.
Displacement of halogens
A more reactive halogen will always displace a less reactive halide from its compounds in solution.
Uses of fluorine and its compounds
Fluoridation of water, to prevent tooth decay
Toothpaste, to prevent tooth decay
Polymers, e.g. Teflon for non-stick pans
Processing uranium nuclear fuel
Uses of chlorine and its compounds
Chlorination of water, to kill microorganisms
To make bleach
Used in the production of paper, paints, plastic products