Group 7(17), the Halogens

Question 1

Describe atomic radius trend in group 7

Answer 1

Increases going down the group

Question 2

Describe the trend in electronegativity in group 7

Answer 2

• Falls down the group
• shielding/increase in atomic radius
• less attraction to nuclues

Question 3

Describe melting and boiling point in Group 7

Answer 3

• Increase down the group
• Van der Waals increase due to bigger size
• more energy to break the forces

Question 4

How do Group 7 molecules exist?

Answer 4

Diatomic w/ covalent bond

Question 5

What is a displacement reaction?

Answer 5

Halogen that is a strong oxidising agent will displace a halogen with a lower oxidising power

Question 6

Describe the displacement reactions of Grp 7 elements C, BR and I

Answer 6

KCL –> no reaction for Br, Iodine and chlorine
KBr —> Cl has a yellow colour, no for Br and I
KI —> Cl brown colour, Br brown colour, Iodine no reaction

Question 7

Describe the oxidising ability of the Halogens

Answer 7

Falls as you go down the group

Question 8

Explain the oxidising ability of the halogens down the group

Answer 8

• ability to attract electrons decrease due to shielding and freater atomic radius
• weaker attraction to accept electrons

Question 9

Describe the reducing power in the halogens

Answer 9

Increases down the group

Question 10

Explain the reducing ability of the halogens

Answer 10

Outer electrons further away than nucleus
less attraction
electrons are donated easily

Question 11

What is the general formula of Halogens and Sulphric Acid

Answer 11

H2SO4 +YX- —> HX + HSO4- + Y+

Question 12

Describe observations with Halogens and Sulphric Acid

Answer 12

F and Cl = steamy white fumes
Br = steamy fumes with brown colour of bromine vapour
Iodide = white steamy fumes; black solid and purple fumes of Iodine

Question 13

How do halogens reduce sulphuric acid

Answer 13

• F and Cl ions won’t reduce conc. sulphric acids
• Br reduces sulphric acid to sulphur dioxide +Br ions oxidised to bromine
• Iodine reduce to mix of protons including hyrogen sulphite/ide + iodine ions are oxidised to iodine

Question 14

Describe the reaction of halogens with hydrogen as a trend

Answer 14

Less vigorous down the group

Question 15

General equation for Group 7 with Hydrogen

Answer 15

H2 + X2 —-> 2HX

Question 16

What is the test for Halide Ions

Answer 16

1. Must be done in a solution (if solid dissolve in pure water)
2. Add Nitric acid
3. The add silver nitrate

Question 17

Why do we add Nitric Acid in the Halide ions test?

Answer 17

Reacts with and removes, other ions that might cause confusing precipitates with silver nitrate

Question 18

Why do we use silver nitrate in the test for halide ions?

Answer 18

Silver nitrate allows precipitates that are characteristically coloured - easier to identify

Question 19

What can you add to distinguish between similar precipitates?

Answer 19

Dilute Ammonia or Concentrated Ammonia

Question 20

How do you identify the halide ions in the test with silver nitrate?

Answer 20

Cl= white p.p 
Br = Pale cream p.p 
I = Pale yellow p.p

Question 21

What are the observations of “halide ions test” with concentrated sulprhic acid

Answer 21

Cl = HCL gas as white fumes
Br = reddish-brown gas 
I = Strong egg smell

Question 22

What is a disproportion reaction?

Answer 22

Same species is both oxidised and reduced

Question 23

The reaction of Cl and H20 to form what?

Answer 23

• Chlorate and Chloride ions

- CL2 +H20 —-> CLO- +CL- + 2H+

Question 24

What can the mixture of NaCL and NaCO make?

Answer 24

bleach and disinfectant