Group 7

The Group 7 elements are all very reactive non-metals. As elements, they are known as 1, but when they exist as ions, they are instead known as 2.

1) halogens

2)halides

Fluorine state and colour at room temperature?

yellow and gas

Chlorine state and colour at room temperature?

green and gas

bromine state and colour at room temperature?

red and liquid

iodine state and colour at room temperature?

black and solid

As we go down Group 7, electronegativity…

decreases

The halogens which are solid at room temperature are…

iodine

astatine

Why does the boiling points of the halogens increase as you go down the group?

more mass

greater size

greater surface area

more electrons

The intermolecular forces which hold molecules like halogens together, and prevent them from becoming gases, are called…

London forces

State the trend in the boiling points of the halogens from fluorine to iodine and explain this trend.

Boiling points increase from fluorine to iodine.

This is because the molecules increase in size / molecular mass / surface area / number of electrons.

This increases the strength of the London forces between molecules.

Therefore, more energy is needed to overcome these forces.

Trend in reactivity as you go down group 7?

decreases

Going down the group, oxidising ability…

decreases

Weaker oxidising agents make stronger reducing agents, so the reducing ability of the halides…

increases down the group

Which reactions take place between fluoride ions and concentrated sulfuric acid?

acid-base reaction

Which reactions take place between bromide ions and concentrated sulfuric acid?

What would we observe?

acid-base reaction

redox reaction

• brown

• steamy or steam or vapour or fumes

When concentrated sulfuric acid is added to sodium iodide salt, we can make several observations.

State the chemical formula of the substance which is observed as steamy fumes.

HI (g)

When concentrated sulfuric acid is added to sodium iodide salt, we can make several observations.
State the chemical formula of the substance which is observed as a black solid.

I₂(s)

When concentrated sulfuric acid is added to sodium iodide salt, we can make several observations.

State the chemical formula of the substance which is observed as a yellow solid.

S(s)

When concentrated sulfuric acid is added to sodium iodide salt, we can make several observations.State the chemical formula of the substance which is observed as the smell of rotten eggs.

H₂S(g)

What is the name given to a halogen that has gained an electron?

halide

Which halide is the strongest reducing agent?

iodide

Which of the following is produced at any point when sodium chloride reacts with concentrated sulfuric acid?

HCl

Which of the following is produced at any point when sodium bromide reacts with concentrated sulfuric acid?

HBr, Br2, SO2

Which of the following is produced during the reaction between sodium iodide and concentrated sulfuric acid?

HI, I₂,SO₂,S,H₂S

Which reactions take place between bromide ions and concentrated sulfuric acid? (2)

acid-base reaction

redox reaction

What would we observe in the reaction between bromide ions and concentrated sulfuric acid?

HBr produces steamy fumes

bromine vapour in the brown clolour of the fumes

When concentrated sulfuric acid is added to sodium iodide salt, we can make several observations.

State the chemical formula of the substance which is observed as steamy fumes.

HI(g)

When concentrated sulfuric acid is added to sodium iodide salt, we can make several observations.

State the chemical formula of the substance which is observed as a black solid.

I2(s)

When concentrated sulfuric acid is added to sodium iodide salt, we can make several observations.

State the chemical formula of the substance which is observed as a yellow solid.

S(s)

When concentrated sulfuric acid is added to sodium iodide salt, we can make several observations.

State the chemical formula of the substance which is observed as the smell of rotten eggs.

H2S(g)

What is the name given to a halogen that has gained an electron?

halide

Which halide is the strongest reducing agent?

Iodide

why does the reducing power of halides increase down the group?

Down the group of halides, reducing power increases.
This trend is explained by the increasing number of electron shells.

This causes the distance between the outer electrons and the nucleus to increase, so that attraction decreases.

Therefore, the electron is more easily lost and donated to another atom which reduces that atom.

State the acid-base reaction when sodium bromide reacts with concentrated sulfuric acid including state symbols

The reaction produces hydrogen bromide and sodium bisulfate. The equation is NaBr(s) + H2SO4(l) → HBr(g) + NaHSO4(s).

Complete the following redox reaction equation for bromide’s reaction with concentrated sulfuric acid:

• 2H⁺ +2Br- + H2SO4(l) → SO₂(g)+2H2O(l)+Br2(l)

State the balanced equation for the reduction of sulphur, from an oxidation state of +6, in concentrated sulfuric acid to an oxidation state of 0 using iodide.

H2SO4+6I^-+6H⁺—> S+3I₂+4H₂O

Complete the balanced equation for the reduction of sulphur, from an oxidation state of +6, in concentrated sulfuric acid to an oxidation state of −2 using iodide.

8H⁺+8I^-+H₂SO₄—>H₂S+4H₂O+4I₂

Which of the following is produced at any point when sodium chloride reacts with concentrated sulfuric acid?

HCl and NaHSO4

Which of the following is produced at any point when sodium bromide reacts with concentrated sulfuric acid?

HBr, Br2,SO2

Which of the following is produced during the reaction between sodium iodide and concentrated sulfuric acid?

HI, I2, H2S, SO2 and S

Silver nitrate reacts with the different halide ions to form silver halides.

what precipitate does Silver fluoride form?

no precipitate

Silver nitrate reacts with the different halide ions to form silver halides.

what precipitate does Silver chloride form?

white precipitate

Silver nitrate reacts with the different halide ions to form silver halides.

what precipitate does Silver bromide form?

cream precipitate

Silver nitrate reacts with the different halide ions to form silver halides.

what precipitate does Silver iodide form?

yellow precipitate

Soluble carbonates and hydroxides would react with silver nitrate to form insoluble precipitates. This would invalidate using silver nitrate as a test to identify halide ions.

In order to prevent these precipitates forming, we acidify the aqueous solution using dilute 1)

This reacts with hydroxides to form 2)

It also reacts with carbonates to form 3)

1)nitric acid, HNO3

2) water, H2O

3)carbon dioxide and water

An aqueous solution was acidified with dilute nitric acid, and silver nitrate solution was then added.

A precipitate formed.

Dilute ammonia solution was then added to the solution, but the precipitate did not dissolve.

Concentrated ammonia solution was then added, but the precipitate still did not dissolve.

Identify the halide ion in the solution.

iodide

The identities of silver halide precipitates can be confirmed using ammonia solution.

First if we add dilute ammonia solution what will happen?

Silver chloride will then dissolve, giving a colourless solution.

The identities of silver halide precipitates can be confirmed using ammonia solution.

Then, we add concentrated ammonia solution what will happen?

Silver bromide will then dissolve, giving a colourless solution.

The identities of silver halide precipitates can be confirmed using ammonia solution. what will happen if we add ammonia to silver iodide?

Silver iodide is insoluble in any concentration of ammonia, and so will remain as a precipitate.

which halide is soluble in water?

fluoride

The reaction of aqueous silver nitrate and aqueous sodium fluoride forms a silver salt that is…

soluble.Therefore, the silver salt wil dissolve

Describe a method that can be used to test which halide a solution contains, given silver nitrate solution and ammonia solution.

Aqueous nitric acid is first added to the solution to remove any carbonate and hydroxide ions as these will form precipitates with silver nitrate, giving a false positive result.



Aqueous silver nitrate is then added to form the silver halide which will precipitate.



If the halide is chloride then a white precipitate will form.

If the halide is bromide then a cream precipitate will form.

If the halide is iodide then a pale yellow precipitate will form.

However, if the halide is fluoride then the precipitate is soluble and will dissolve instead.



Sometimes the colour of the precipitate is difficult to distinguish so different concentrations of ammonia can be used.



In dilute ammonia, the chloride precipitate will dissolve.

In concentrated ammonia, the chloride and the bromide precipitates will dissolve.

The iodide precipitate will not dissolve in either dilute or concentrated ammonia.