Periodic table Group 17

Question 1

Bond dissociation energy down the group

Answer 1

BDE decreases (BDE is intramolecular btw)
Down the group,
- Less effective orbital overlap between bonding orbitals
- Halogen-halogen bond becomes weaker
(Except F2)

Question 2

Volatility down the group (tendency to evaporate at normal temperature)

Answer 2

Down the group:
- size of electron cloud increases
- electron cloud becomes more easily polarisable
- instantaneous dipole-induced dipole interactions become stronger
- more energy is required to break apart intermolecular forces of attraction
- volatility decreases

Question 3

Displacement reactions

Answer 3

A more reactive/oxidising halogen displaces a less reactive/oxidising halogen from its compound.
Basically, the elements above can displace the elements below.

Question 4

Thermal stability of hydrogen halides

Answer 4

Thermal stability decreases from HF>HCL>HBr>HI
- thermal stability depends on the H-X bond strength
- more endothermic bond dissociation energy suggests that H-X bond is stronger and HX is more thermally stable. (With reference to the data booklet)
= bond dissociation energy of H-X decreases in the order H-F > HCl> HBr > HI
- thermal stability hence decreases in the same order

Why H-X bond strength decreases down Group 17:
- down grp 17
- less effective orbital overlap between 1s orbital of hydrogen and the valence p orbital of the halogen + EN difference between and halogen decreases - decrease in bond polarity
- H-X bond strength decreases

Question 5

Thermal stability of hydrogen halides

Answer 5

Thermal stability decreases from HF>HCL>HBr>HI
- thermal stability depends on the H-X bond strength
- more endothermic bond dissociation energy suggests that H-X bond is stronger and HX is more thermally stable. (With reference to the data booklet)
= bond dissociation energy of H-X decreases in the order H-F > HCl> HBr > HI
- thermal stability hence decreases in the same order

Why H-X bond strength decreases down Group 17:
- down grp 17
- less effective orbital overlap between 1s orbital of hydrogen and the valence p orbital of the halogen + EN difference between and halogen decreases - decrease in bond polarity
- H-X bond strength decreases

Question 6

Testing for halide ions

Answer 6

Add AgNO3, add excess NH3 (aq)
Cl-(aq): white ppt of AgCl, Ppt soluble in NH3
Br-(aq): pale cream ppt of AgBr, ppt partially soluble in NH3
I- (aq): yellow ppt of AgI, ppt insoluble in NH3