Chapter 12: Group 17

Chapter 12:
Group 17

Group 17 : F, Cl, Br, I, At

Physical properties Chemical properties

1. Colour and Physical state 1. Relative reactivity of Group 17
(a) at room temperature and elements as oxidising agent
pressure
(b) in the gaseous state, 2. (a) Reaction with Hydrogen, H2 to
aqueous solution and form hydrogen halides
organic solvent, CCl4
2. (b) Thermal stability of hydrogen
2. Melting point / Boiling Point halides, HX

3. Volatility 3. Reaction of chlorine, Cl2 with aqueous
sodium hydroxide :
cold, dilute vs Hot concentrated

4. Reaction of halide ions with silver
nitrate followed by aqueous ammonia,
NH3

5. Reaction of halide ions with
concentrated H2SO4

Chapter 12: Group 17

12.1 Physical Properties Of Group 17 Elements

1. Colour and Physical state at room temperature and pressure

Group 17 Elements Colour Colour becomes
Pale yellow gas darker
Fluorine, F2 Yellowish green gas
Chlorine, Cl2 Reddish brown liquid
Bromine, Br2 Shiny black solid
Iodine, I2

2. Colour of Cl2, Br2 and I2 in the gaseous state, aqueous solution and CCl4
solvent is shown below:

Colour of halogen in

Halogen Gaseous state Aqueous solution CCl4
Chlorine, Cl2 Yellowish green
Bromine, Br2 Reddish Brown Pale yellow-green Pale yellow-green

Iodine, I2 Purple Reddish Brown Reddish Brown

Brownish-orange Violet

Chapter 12: Group 17
12.1 Physical Properties Of Group 17 Elements

2. Melting point / Boiling Point

Fluorine, F2 Boiling Point/ Melting Point
Chlorine, Cl2 increases going Down Group 17
Bromine, Br2
Iodine, I2 • F2, Cl2, Br2 and I2 are simple covalent molecule with weak
intermolecular van der Waals forces.

• Molecular size increases from F2, Cl2, Br2 to I2 .
• No. of electron per molecule increases from F2, Cl2, Br2 to

I2 .
• Strength of intermolecular van der Waals forces becomes

stronger from F2, Cl2, Br2 to I2 .

• More energy is required to overcome the intermolecular
forces .

• Melting point / boiling point increases from F2, Cl2, Br2 to
I2 .

Chapter 12: Group 17

12.1 Physical Properties Of Group 17 Elements

3. Volatility

Volatility of halogens decreases
going Down Group 17

Fluorine, F2 • F2, Cl2, Br2 and I2 are simple covalent molecule with weak
Chlorine, Cl2 intermolecular van der Waals forces.
Bromine, Br2
Iodine, I2 • Molecular size increases from F2, Cl2, Br2 to I2 .
• No. of electron per molecule increases from F2, Cl2, Br2 to

I2 .
• Strength of intermolecular van der Waals forces becomes

stronger from F2, Cl2, Br2 to I2 .

• Tendency of molecules to vaporized from liquid to vapour
decreases.

• Volatility decreases from F2, Cl2, Br2 to I2 .

Chapter 12: Group 17
12.2 Chemical Properties Of Group 17 Elements

1. Relative reactivity of Group 17 elements as oxidising agent
(a) Compare standard electrode potential
The more positive the Eoreduction, the stronger the oxidising power.

Oxidizing Reducing
strength strength
INCREASES INCREASES

(b) Compare size of halogen atoms

The smaller the size of halogen atom,
the higher the tendency for halogen atom to accept electron.
The stronger the oxidising strength.



Chapter 12: Group 17
12.2 Chemical Properties Of Group 17 Elements

2 (a) Reaction with Hydrogen, H2 to form hydrogen halides
Halogen reacts with hydrogen to form hydrogen halide, HX.

H2(g) + X2(g) → 2 HX(g)
Reactivity decreases going down group 17.

Chapter 12: Group 17
12.2 Chemical Properties Of Group 17 Elements
2 (b) Thermal stability of hydrogen halides, HX

2 HX(g) H2(g) + X2(g)

Thermal stability of HX decreases from HCl, HBr to HI.

HCl > HBr > HI

Thermal stability decreases

Explanation:

Size of halogen atom becomes bigger from Cl, Br to I.

H-X bond length becomes longer and weaker from H-Cl, H-Br to H-I.

Less heat is needed to break the covalent bond from H-Cl, H-Br to H-I.
H-X bond becomes easier to break from H-Cl, H-Br to H-I

Hence, thermal stability of HX decreases from HCl, HBr to HI.

Chapter 12: Group 17

12.2 Chemical Properties Of Group 17 Elements

3. Reaction of chlorine, Cl2 with aqueous sodium hydroxide
(a) cold, dilute NaOH(aq)
Cl2 (g) + 2NaOH (aq) → NaCl (aq) + NaClO(aq) + H2O(l)

ClO- = chlorate(I) ion

(b) hot, concentrated NaOH(aq)

3 Cl2(g) + 6NaOH(aq) → 5NaCl(aq) + NaClO3 (aq) + H2O(l)

ClO3- = chlorate(V) ion

Note:

(1) Both reactions are disproportionation reaction.
(2) Chlorate(I) ion, ClO- ion is unstable at high temperature. It will

disproportionate to ClO3- and Cl- ion.

+1 -1 +5

3NaClO(aq) 2NaCl(aq) + NaClO3 (aq)

Chapter 12: Group 17
12.2 Chemical Properties Of Group 17 Elements

4. Reaction of halide ions with silver nitrate followed by aqueous

ammonia, NH3

(a) Chloride ion NH3(aq)
Cl-(aq) + Ag+(aq) → AgCl (s)
[Ag(NH3)2]+(aq)
White precipitate formed Colourless solution

(b) Bromide ion Dilute NH3(aq) Insoluble

Br-(aq) + Ag+(aq) → AgBr (s) Concentrated NH3(aq) [Ag(NH3)2]+(aq)
Cream / pale yellow Colourless solution
precipitate formed
Dilute NH3(aq) Insoluble
(c) Iodide ion
Concentrated NH3(aq) Insoluble
I-(aq) + Ag+(aq) → AgI (s)
Yellow precipitate formed



Chapter 12: Group 17
12.2 Chemical Properties Of Group 17 Elements
5. Reaction of halide ions with concentrated H2SO4

Chapter 12: Group 17
12.2 Chemical Properties Of Group 17 Elements
5. Reaction of halide ions with concentrated H2SO4

Chapter 12: Group 17
12.3 Industrial Applications of Halogen And Their Applications

Chapter 12: Group 17
12.3 Industrial Applications of Halogen And Their Applications

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