3.1.3 The Halogens - Chemistry A Level Practice Flashcards

A set of flashcards covering physical properties, reactivity trends, displacement reactions, and disproportionation reactions of the Halogens based on the A Level Chemistry curriculum.

Why do the boiling points of the halogens Cl2, Br2, and I2 increase down the group?

As you go down the group, the number of electrons increases, leading to stronger induced dipole–dipole interactions (London forces) which require more energy to break.

What is the outer-shell electron configuration of the halogens?

The outer-shell configuration is $s^2p^5$.

In terms of redox reactions, how do halogen atoms typically achieve a stable electron arrangement?

Halogens act as oxidising agents and typically gain one electron to form $1-$ ions.

Explain the trend in reactivity and oxidising power as you descend Group 7.

Reactivity decreases down the group because the atomic radius and electron shielding increase, which decreases nuclear attraction and makes it more difficult to gain an electron.

What is the definition of disproportionation?

Disproportionation is a reaction in which the same element is both oxidised and reduced.

Write the chemical equation for the reaction of chlorine with water used in water purification.

$$Cl_2(g) + H_2O(l) \rightarrow HCl(aq) + HOCl(aq)$$

What are the required conditions for chlorine to react with aqueous sodium hydroxide to form bleach?

The reaction requires cold and dilute aqueous sodium hydroxide ($NaOH$).

State the reaction equation and observations for chlorine reacting with potassium bromide solution.

$Cl_2(g) + 2Br^-(aq) \rightarrow 2Cl^-(aq) + Br_2(aq)$. The pale green solution turns orange; on addition of an organic solvent, the solution turns red.

What color does iodine produce in an organic solvent like cyclohexane?

Iodine produces a violet or purple color in organic solvents.

What is the benefit of adding chlorine to water treatment systems?

The chlorate ion ($OCl^-$) formed acts as a weak bleach that kills bacteria.

What are two risks associated with using chlorine in water treatment?

Chlorine gas is toxic in excess and can react with hydrocarbons to form chlorinated hydrocarbons, which are carcinogens.

Describe the observation when iodine is in an aqueous solution versus an organic layer.

Iodine is brown in aqueous solution and violet or purple in the organic layer.

What would be the expected observation if bromine was added to a solution of sodium iodide?

The solution would change to brown due to the displacement of iodide ions to form iodine: $Br_2(aq) + 2I^-(aq) \rightarrow 2Br^-(aq) + I_2(aq)$.

Why would the halogen astatine be expected to react similarly to other halogens?

It has the same number of valence electrons in its outer shell, resulting in similar chemical properties.

What happens when blue litmus indicator is added to aqueous chlorine?

The litmus indicator will turn red due to the acid ($HCl$ and $HOCl$) and then turn colourless due to the bleaching effect of the chlorate ion.