Group 17

Question 1

What are some basic properties of halogens

Answer 1

1. Most chemistry has elements in -1 oxidation state as are normally more electronegative
2. All form diatomic X2 molecules
3. All weaker oxidising agents than F2
4. All have stronger X-X bonds than F2

Question 2

Describe F2

Answer 2

1. Pale yellow gas
2. V corrosive
3. Most reactive element known- handles in Teflon or special steel vessels

Question 3

Describe Cl2

Answer 3

1. Pale green gas

Question 4

Describe Br2

Answer 4

1. Brown/ orange liquids

Question 5

Describe I2

Answer 5

1. Purple crystals

Question 6

What are unique properties of F

Answer 6

1. Strongest oxidising agents of all the halogens
2. DHea is out of order- smaller than Cl
3. Weak F-F bond so are kinetically reactive
4. Hydride complexes show unusual H-Bonding effects

Question 7

Describe the difference in bond strengths down the group

Answer 7

1. F-F bond is small so lots of LP repulsion making it unstable and weak
2. Cl is bigger- so Cl-Cl is longer, as orbitals are more diffuse also the repulsion is lessened- bond strength max
3. As we go to bigger elements the repulsion between L.Ps drops off as the length of the E-E bond becomes the important thing and as we go down the group the natural order continues.

Question 8

Describe HF

Answer 8

1. Strongest H bond
2. But low bp - 1D nature of HF unlike H2O
3. Some of the H bonding is retained at relatively high temperatures- don’t need to break it all up

Question 9

What happens to acidity down the group

Answer 9

1. Increases as bond strength decreases

Question 10

What are the reasons HF is the least acidic

Answer 10

1. Strong H-F bond- harder to break
2. Can get stuck at ion pair which stops complete [h3o]+ and F- dissociation
3. [HF2]- in an additional equilib- HF + F- [HF2]- - lower [HF] in solution so lower acid strength

Question 11

What are interhalogen compounds

Answer 11

1. Prepared by direct combination of elements
2. e.g. CIF3 + F2 –> ClF5
3. Highly reactive
4. Poperties intermediate between those of the elements
5. Y-F bonds are usually more stable than corresponding Y-Cl bonds
6. IF is most stable due to polar contribution

Question 12

What are the 4 families of interhalogen compounds

Answer 12

1. XY
2. XY3
3. XY5
4. XY7