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
VII
F
Cl
• First Ionisation energy
– Decreases down group
Br
• First Electron Affinity
– Decreases down group
I
• Electronegativity.
– Decreases from F - I
At
Compounds
• Solubility
–
–
–
–
–
–
–
–
Chlorine and Bromine are fairly soluble in water
They react reversibly
Cl2 +H2O  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- ions
– With group I & II
• Ionic bonding
– 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