Group 7

Question 1

State and explain the trend of electronegativity in G7?

Answer 1

Electeronegativity decreases down the group
There are more full shells of electrons down the group
This increases shielding
So there is a greater distance between the outer electrons and the nucleus
This outweighs the nuclear charge and so there is less attraction between the nucleus and outer shells

EG in ICl. Cl is more electronegative than I so electrons are on avg, closer to Cl

Question 2

State and explain the trend of BP in G7?

Answer 2

• The boiling point increases down the group
• Halogens have more mass, more electrons and greater size down the group
• Halogens are held together by Van der Waals, as the electrons increase VdW also increases

And more energy is required to overcome these forces

Question 3

Explain the trend of oxidising ability of halogens

Answer 3

• Oxidising ability reduces down the group
• Halogens become halide ions in redox reactions
• Electrons are transferred so the halogens act as oxidising agents
• So the halogens at the top of the group can displace all the elements below it

Question 4

Explain the trend in reducing ability in G7?

Answer 4

• Reducing ability increases down the group
• Weak oxidising agents make strong reducing agents
• Eg I,Br and Cl reduces F2

Question 5

What is the product in a silver nitrate reaction to identify halides?

Answer 5

AgF - no precipitate
AgCl - white precipitate
AgBr - cream precipitate
AgI - pale yellow precipitate

Question 6

Explain why nitric acid is added to the silver nitrate test

Answer 6

Because the presence of CO3 or OH- ions may result in the production of AgCO3 or AgOH
Nitric acid reacts with OH and Co3 to produce water and CO2/water

AgCO3 and AgOH are insoluble so they would form a precipitate invalidating the results of the AgNO3 results

Question 7

How can dilute ammonia be used to identify halides?

Answer 7

With the addition of dilute ammonia
AgCl - dissolves