Chemistry - Halogens

Halogens

Group 7 elements in the periodic table; have 7 electrons in their outer shell and form salts with metals.

What does the term ‘halogen’ mean?

Salt former.

Properties of Halogens

Typical non-metals; poor conductors of electricity and heat, low density, low melting and boiling points.

Diatomic molecules

All halogens exist as diatomic molecules (e.g., F2, Cl2, Br2, I2) meaning two atom molecules

Iodine's vapor

Iodine forms a purple vapour when warmed.

Fluorine

formula F2, state: gas, colour of vapour: yellow,

Chlorine

formula Cl2, state: gas, colour of vapour: green

Bromine

formula Br2, state: liquid, colour of vapour: orange/brown

Iodine

formula I2, state: solid, colour of vapour: purple/grey,

Trend in states of halogens

As you go down Group 7, the state changes from gas to liquid to solid. Melting and boiling points increase

Reactivity of halogens

Halogens decrease in reactivity as you go down the group this is because as you go down the group the outer shells becomes further from the nucleus this weakens the attractive force making it harder to gain electrons; fluorine is the most reactive.

Displacement reactions

A more reactive halogen displaces a less reactive halide ion from its solution.

Chlorine and iron reaction

Chlorine reacts with iron to produce iron (III) chloride, needs small heat to react.

Bromine and iron reaction

Bromine reacts with iron to produce iron (III) bromide, needs small heat, but slower than chlorine.

Iodine and iron reaction

Iodine reacts with iron to produce iron (III) iodide, needs several minutes of heating.

Uses of Halogens

Chlorine - water supplies, swimming pools, bleaches

Bromide - plasters, sterilising sprays

Iodide - antiseptic

Safety precaution

Fume cupboard used for reactions – halogens produce toxic vapours.

Displacement

A decrease in reactivity down the halogen group means that a more reactive halogen can displace a less reactive one

Fluorine displaces chlorine, bromine and iodine

Chlorine displaces bromine and iodine

Bromine displaces iodine

Iodine doesn’t displace any halogen

e.g Cl2 + 2KBr → Br2 + 2KCl

Ionic bonds with metals

When a halogen gains an electron to form a -1 ion it is called a halide meaning the names of halogens change to e.g chloride which is an ion