Section 2 10 Group 7, the halogens

Properties of Halogens

• Diatomic

• Going down the group the atomic radius increases

• The electronegativity decreases going down the group

• The MP and BP increases going down the group, due to van der waals forces.

• G,G,L,S => F, Cl, Br, I

Why is the bond enthalpy of F-F weak?

• The small size of fluorine atom, leads to repulsion between the non-bonding electrons because they are close.

The trends of oxidising ability going down group 7:

• The oxidising ability of the halogens increases going up the group. They tend to get more reduced.

  • This is where a more reactive halogen F> Cl > Br > I gets displaced from a less reactive halogen.

The trends of reducing power of the halides:

Going down the group the reducing power increases.

Sodium chloride and concentrated sulfuric acid

• No redox reaction takes place, only acid-base reaction

• Because Chlorine is a weak reducing agent

Sodium Bromide and concentrated sulfuric acid

• Acid base and redox reaction

• Bromine reduces Sulfur from +6 to +4

  • Observations: A red-brown fumes

Sodium Iodide and concentrated sulfuric acid

• Acid base and redox reaction

• Iodine reduces Sulfur from +6 to -2

  • Hydrogen sulfide rotten eggs smell

  • Iodine black or grey solid

  • Purple stemy fumes

Chlorine reaction with water with no sun

This reaction is a disproportionation reaction, as Chlorine gets reduced and oxidised.

Chlorine reaction with water with sunlight

Chlorine reaction with alkali (Sodium hydroxide)

NaClO where the ClO ions is used to kill microorganism