3.1.3 - The Halogens
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What group elements are referred to as Halogens?
Group 7
List 2 properties of Halogens
Low melting and boiling points Exist as diatomic molecules
What is the trend in boiling point down group 7? Why?
Increases down the group because: Size of atom increases as more occupied electron shells —> stronger london forces of attraction between molecules, take more energy to break
What is the trend in reactivity down group 7? Why?
Reactivity decreases because: Atomic radius increases Electron shielding increases Ability to gain an electron and form 1- ions decreases
What is the trend in oxidising ability down the group? Why?
Decreases down group Cl strongest, I weakest This is because Cl has the fewest occupied electron shells, the greatest force of attraction between outer electrons and nucleus and thus is the easiest to gain electrons and be reduced —> best oxidising agent
What is the trend in reducing ability of the halides down the group? why?
Increases down the group Cl- weakest, I- strongest This is because I- has the most occupied electron shell so outer electrons are further from the nucleus, weakest force of attraction between outer electrons and positive charge of nucleus and thus is the easiest to be oxidised and lose electrons –> best reducing agent
When a more reactive halogen displaces a less reactive halide, what is the reaction called?
Displacement reaction
What is the colour of chlorine in water?
Pale green
What is the colour of bromine in water?
Orange
What is the colour of iodine in water?
Brown
What is the colour of chlorine in cyclohexane
Pale green
What is the colour of bromine in cyclohexane
Orange
What is the colour of iodine in cyclohexane
Violet
Out of the 3 halides Cl-, Br- and I-, which one of these can be oxidised by chlorine?
Br- and I- ions
Write the equation for chlorine oxidising bromide ions
Cl2 (aq) + 2Br- (aq) —> 2Cl- (aq) + Br2 (aq)
Write the equation for Cl2 oxidising 2I-
Cl2 (aq) + 2I- (aq) ——-> 2Cl- (aq) + I2 (aq)
Out of the 3 halides Cl-, Br- and I-, which one of these can be oxidised by bromine?
I- ions
Write the equation for bromine oxidising iodide ions
Br2 (aq) + 2I- (aq) —–> 2Br- (aq) + I2 (aq)
Out of the 3 halides Cl-, Br- and I-, which one of these can be oxidised by iodine?
Does not oxidise Cl- or Br-
Define disproportionation
The oxidation and reduction of the same element in a redox reaction
What is the equation for the reaction of Cl2 with water?
Cl2 (g) + H2O (l) —> HClO (aq) + HCl (aq)
What type of reaction is the reaction of chlorine with water?
Disproportionation Chlorine is both oxidised and reduced
Why is chlorine added to drinking water?
It kills the bacteria in the water and makes it safer to drink
What are the two forms of the chlorate ion?
ClO- is chlorate (l) ClO3- is chlorate (V)