This document summarizes the physical and chemical properties of Group VII (halogen) elements. It describes their: 1) Colors and states - the halogens range from pale yellow gas (F2) to black solid (I2). 2) Reactivity trends - fluorine is the strongest oxidizing agent while iodine is the weakest. Fluoride is the weakest reducing agent and iodide is the strongest. 3) Reactions with silver nitrate and ammonia - these tests can be used to identify halide ions based on solubility differences of the precipitates formed.

1. Group VII

2. Group VII
The focus for Inorganic Chem (Gp II, VII, Transition
Elements) is the trends for the physical and
chemical properties of the elements.

4. Physical Properties
Colour/ State
It is important to memorise the colour/ state of halogens
as it is often needed for identification of unknown
halogens.

5. Physical Properties
X2
State at rtp
F2
Pale yellow gas
Colour in water Colour in organic
solvents (e.g hexane)
-
Cl2
Yellow green gas
-
Yellow green
Br2
Dark red liquid
Brown
Brown
I2
Black solid
Brown
Violet

6. Physical Properties
bp/ mp
- X2 are have simple molecular structures with dispersion
forces between molecules
- Boiling/ melting involves overcoming these
intermolecular dispersion forces
- Strength of dispersion forces depends on Mr (size of e–
cloud)

7. Physical Properties
Solubility
- Being non-polar molecules, X2 are insoluble in water
(polar solvent)
- However, they can ‘dissolve’ by undergoing reaction
with water or ions which may be present in water:
Cl2 + H2O ⇌ HOCl + HCl
I2 + I– ⇌ I3–

8. Chemical Properties
- Halogens are oxidising agents
Down the group
- Oxidising ability ↓
- Reactivity ↓
F2 is the strongest oxidising agent amongst the halogens;
F− is the weakest reducing agent amongst the halides
I2 is the weakest oxidising agent amongst the halogens;
I− is the strongest reducing agent amongst the halides

9. Chemical Properties
4 Cl2 + S2O32− + 5H2O → 8 Cl− + 10 H+ + 2 SO42−
4 Br2 + S2O32− + 5H2O → 8 Br− + 10 H+ + 2 SO42−
I2 + 2 S2O32− → 2I− + S4O62−
this is the rxn in iodometric titrations.
Cl2 and Br2 oxidises S2O32− (-2) to SO42− (+6) while I2 can only
oxidise S2O32− (-2) to S4O62− (-1)

10. Chemical Properties
Displacement
- A more reactive halogen can displace the less reactive
halogen from its aqueous halide ions.
- Reaction is redox in nature.

11. Chemical Properties
Reaction with H2
- H2 + X2  2HX
- X2 that is more strongly oxidising will give rise to a more
vigorous reaction

12. Chemical Properties
Stability of HX
- HX can decompose on heating: 2HX  H2 + X2
- Note that decomposition breaks the H–X covalent bond
- The stronger the bond, the greater the thermal stability of
the HX

13. Chemical Properties
Stability of HX
Recall:
- Strength of covalent bonds depends on atomic radius of
overlapping atoms (chemical bonding)
- Boiling overcomes intermolecular bonds; decomposition
overcomes intramolecular bonds (Gp II)
- Be clear what the qns is asking for. Student often give the
wrong factors/ explanations

14. Chemical Properties
Halide
+ AgNO3 (aq)
+ NH3
Cl– (aq)
white ppt
soluble in aq NH3
Br– (aq)
cream ppt
insoluble in aq NH3; soluble in conc
NH3
I– (aq)
yellow ppt
insoluble in aq NH3 and conc NH3
Ag+ + X–  AgX
(s)
AgX (s) ⇌ Ag+ + X–
Ag+ + 2NH3 ⇌ [Ag(NH3)2]+

15. Chemical Properties
Halide + conc H2SO4
Cl–
NaCl (s) + H2SO4 (aq)  HCl (g) + NaHSO4 (aq)
white fumes (HCl) observed
Br–
NaBr (s) + H2SO4 (aq)  HBr (g) + NaHSO4 (aq)
2HBr (g) + H2SO4 (aq)  Br2 (g) + SO2 (g) + 2H2O (l)
orange fumes (Br2) observed; pungent gas (SO2) liberated
I–
NaI (s) + H2SO4 (aq)  HI (g) + NaHSO4 (aq)
8HI (g) + H2SO4 (aq)  4I2 (g) + H2S (g) + 4H2O (l)
violet fumes (I2) observed; pungent gas (H2S) liberated

16. Chemical Properties
- I– being the most strongest reducing can reduce H2SO4
(+6) to H2S (-2)
- It is important to memorise the observations and
equations for the reactions.