The Halogens Group VII

Group VII • • Known as halogens – – Derived from Greek, Salt maker React with metals to form salts Astatine doesn’t really exist for a long enough time to explore its chemistry – we predict its reactions by observing trends

VII

F Cl Br I At

At RTP • • • • Fluorine – Pale yellow gas Chlorine – – Pale green gas Bleaches damp litmus Bromine – Brown Liquid (evaporates easily to a brown gas) – Does nasty things to skin!

Iodine – Dark grey / black crystals – Sublimes to a violet vapour on gentle heating

VII

F Cl Br I At

Properties • • • • • • Electron configuration – 5 p electrons.

Atomic Radius – Increases down the group Ionic radius – Increases down the group First Ionisation energy – Decreases down group First Electron Affinity – Decreases down group Electronegativity.

– Decreases from F - I

VII

F Cl Br I At

Compounds • Solubility – – – – Chlorine and Bromine are fairly soluble in water They react reversibly Cl 2 +H 2 O  HCl + HOCl Aqueous solutions are called Chlorine or Bromine water – Chlorine water is (just about) pale green – Bromine water is orangey brown – red – Iodine is only slightly soluble in water – Halogens are much more soluble in hexane.

VII

F Cl Br I At

Bonding in halogens • Ionic Bonding – All the Halogens form X – With group I & II • Ionic bonding – ions With group III • Aluminium fluoride – Ionic • Aluminium chloride varies depending on whether it is anhydrous or not.

– With d-block metals • Covelant when anhydrous • Ionic with water.

Bonding in halogens • • • Covalent Bonding – Polar covalent bonds with almost all non metals – Fluorine is always in the -1 oxidation state – Chlorine is in the -1 oxidation state unless bonded with fluorine or oxygen Halogens other than fluorine have empty d-orbitals so it is possible to promote electrons from the p-orbital into the energetically similar d-orbital This allows more than one covalent bond to be formed.

– This only happens when bonded to a small very electronegative atom such as oxygen.

Reactions of the Halogens • Reactions with Metals

Reactions of the Halogens • Reactions with phosphorus

Reactions of the Halogens • Reactions with solutions of other halides

Reactions of the Halogens • Reactions with water

Reactions of the Halogens • Reactions with alkali

Reactions of the Halogens • Reactions with reducing agents

Reactions of the Halogens • Reactions with sodium thiosulphate

Hydrogen Halides