AQA Chemistry A-level: Group 7

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Questions and Answers

What is the trend in atomic radius of group 7 elements down the group?

It remains constant down the group

It increases down the group (correct)

It decreases down the group

It oscillates down the group

What is the reason for the decrease in reactivity of group 7 elements down the group?

The strength of the van der waals forces increases

The positive attraction of the nucleus is weakened by additional shielding (correct)

The first ionisation energy of the elements increases

The atomic radius of the elements increases

What is the trend in boiling point of group 7 elements down the group?

It decreases down the group

It increases down the group (correct)

It remains constant down the group

It oscillates down the group

What is the trend in oxidising power of group 7 elements down the group?

It decreases down the group Signup and view all the answers

What is the reason for the ability of a halogen to displace any halide beneath it in the Periodic Table?

The relative oxidising strengths of the halogens Signup and view all the answers

What type of molecules are formed by group 7 elements?

Simple covalent molecules Signup and view all the answers

What is the reason for the decrease in reactivity of group 7 elements with an increase in atomic radius?

The positive attraction of the nucleus is weakened by additional shielding Signup and view all the answers

What is the trend in the first ionisation energy of group 7 elements?

It is not applicable to group 7 elements Signup and view all the answers

Which of the following halide ions has the highest reducing power?

Iodide ions Signup and view all the answers

What is the purpose of adding ammonia to the precipitates formed in the reaction of acidified silver nitrate with halide ions?

To distinguish between the different halide ions Signup and view all the answers

Which of the following is NOT a characteristic of halide ions?

Good oxidizing agents Signup and view all the answers

What is the oxidation state of chlorine in Chlorate(I) ions?

+1 Signup and view all the answers

What is the type of reaction that occurs when chlorine reacts with cold water to produce Chlorate(I) ions and chloride ions?

Disproportionation reaction Signup and view all the answers

Which of the following precipitates is formed when acidified silver nitrate reacts with iodide ions?

Yellow precipitate Signup and view all the answers

What is the reason for the increasing reducing power of halide ions down the group?

Due to the increasing shielding Signup and view all the answers

Which of the following is a characteristic of the reaction of acidified silver nitrate with halide ions?

A coloured precipitate is formed Signup and view all the answers

What is the byproduct of chlorine decomposing water in the presence of UV light?

Hydrochloric acid and oxygen Signup and view all the answers

What is the primary purpose of adding chlorine to water treatment processes?

To kill bacteria and other microorganisms Signup and view all the answers

What is the key ingredient produced by mixing chlorine with cold, aqueous sodium hydroxide?

Sodium hypochlorite Signup and view all the answers

What is the purpose of acidifying silver nitrate when testing for halide ions?

To remove impurities that could form a precipitate Signup and view all the answers

What is the characteristic of a substance that contains hydroxide ions?

It is alkaline and turns litmus blue Signup and view all the answers

What happens when an acid is added to a substance containing carbonate ions?

The substance fizzes and produces CO2 gas Signup and view all the answers

What is the purpose of bubbling CO2 gas through limewater?

To confirm the presence of CO2 gas Signup and view all the answers

What is the color of the precipitate formed when chlorine ions react with silver nitrate?

White Signup and view all the answers

Study Notes

Group 7 - The Halogens

Group 7 elements are highly reactive non-metals that need to gain an electron to form a 1- ion and achieve a full outer shell of electrons.
Atomic radius increases down the group due to additional electron shells.

Trends in Properties

Reactivity decreases down the group as atomic radius increases, making it harder to attract an electron.
Ionisation energy decreases down the group due to a greater atomic radius and increased shielding.
Boiling point increases down the group as the strength of van der Waals forces increases with increasing atomic radius.

Oxidising Power

Halogens act as good oxidising agents, accepting electrons from the species being oxidised and being reduced.
Oxidising power decreases down the group as the ability to attract electrons decreases due to shielding and a greater atomic radius.
A halogen will displace any halide beneath it in the Periodic Table.

Halide Ions

Halide ions are good reducing agents, donating electrons to the species being reduced and being oxidised.
Reducing power increases down the group as electrons are easier to lose from larger ions due to shielding and a larger atomic radius.

Testing for Halide Ions

Acidified silver nitrate is used to test for halide ions, forming different coloured precipitates depending on the ion present.
The precipitates can be further tested using ammonia.

Chlorine and Chlorate(I) ions

Chlorine reacts with cold water to produce Chlorate(I) ions (ClO-) and chloride ions.
Chlorine decomposes water to produce oxygen and hydrochloric acid in the presence of UV light.

Uses of Chlorine

Chlorine is used in small quantities to kill bacteria in water treatment processes.
Chlorine can be mixed with cold, aqueous sodium hydroxide to produce sodium hypochlorite, a key ingredient in the production of bleach.

Tests for Ions

Halides are tested for using acidified silver nitrate and ammonia.
Sulfate (SO4²-) is tested for using BaCl2, which reacts to form a white precipitate.
Hydroxide (OH-) is identified using red litmus, which turns blue, or using universal indicator, which turns blue-purple.
Carbonate (CO3²-) is tested for by adding an acid such as HCl, which produces effervescence and CO2 gas, which can be collected and bubbled through limewater to confirm it as carbon dioxide.

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Description

Detailed notes on Group 7 elements, including trends in properties, covering AQA Chemistry A-level curriculum.

AQA Chemistry A-level: Group 7 - The Halogens