3.1.3 Halogens Flashcards
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, greatest force of attraction between outer electrons and nucleus
- Cl 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 shells
- Outer electrons are further from the nucleus
- Weakest force of attraction between outer electrons and positive charge of nucleus
- I⁻ 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⁻ & 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 chlorine oxidising iodide ions.
- Cl₂ (aq) + 2I⁻ (aq) -> 2Cl⁻ (aq) + I₂ (aq)
Out of the 3 halides Cl⁻, Br⁻ & 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⁻ & 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 chlorine 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 (I)
- ClO₃⁻ is chlorate (V)
What is the equation for forming bleach?
- Cl₂ (aq) + 2NaOH (aq) -> NaCl (aq) + NaClO (aq) + H₂O (l)
- NaClO is bleach
