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GROUP 17

ELEMENTS

F

Cl

Br

I

At

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The elements in Group 17 are called halogens, non-metals and exists

as diatomic molecules

PHYSICAL PROPERTIES

ELEMENT Fluorine Chlorine Bromine Iodine

Effective

nuclear charge

7 7 7 7

Atomic radius 0.072 0.099 0.196 0.213

Ionic radius 0.135 0.180 0.195 0.215

Melting point -219 -101 -7.2 114

Boiling point -188 -34.7 58.8 184

Physical state Pale yellow

gas

Pale yellowish

green gas

Reddish brown

gas

Black solid

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Atomic radii / Ionic radii-Decrease with increasing atomic number

Volatility

-Decreased down the group

Melting & boiling point

- Simple structure-Intermolecular forces- Van der Waals Forces

-Increase as increasing molecular mass

--greater no. of electron, Van der Waals forces becomes stronger

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

All hydrogen halides are colourless, acidic gases and dissolve in waterreadily.

The reactivity of the halogen decreases on descending the group as

shown by the fact that the reaction become less vigorous and the reaction

rates become slower

F2(g) + H2(g) 2HF (g) H = -542 kJ

in dark

Cl2(g) + H2(g) 2HCl (g) H = -184 kJ

diffuse sunlightBr2(aq) + H2(g) 2 HBr (g) H = -72 kJ

200C, platinum catalyst

I2(g) + H2(g) 2HI (g) H = +54 kJ

400C, platinum catalyst

Order of reactivity F2< Cl2< Br2< I2

REACTION WITH HYDROGEN

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As the halogens becomes more reactive, the reaction becomes more

exothermic F2is more reactive because the F-F bond is very weak and

H-F bond is very strong

Thermal stabilities of hydrides depends on the bond energy2HX (g) H2(g) + X2(g)

THERMAL STABILITY OF HX

Hydrides Bond length / nm Bond energy / kJmol-1

HF 0.092 562

HCl 0.127 431

HBr 0.141 366

HI 0.161 299

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With hot concentrated sodium hydroxide,70C

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

Sodium chlorate (V)

0 oxidised +5

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

0 reduced -1

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The reaction of halides ions with aqueous silver ions produced a

coloured precipitate

Ag+(aq) + Cl-(aq) AgCl (s)

white

Ag+(aq) + Br-(aq) AgBr (s)

cream

Ag+(aq) + I-(aq) AgI (s)

yellow

Silver chloride dissolves in both dilute and concentrated ammonia to

produce a colourless solution by forming the water-soluble complex ion.

AgCl (s) + 2NH3(aq) [Ag(NH3)2]+

(aq) + Cl-

Silver bromide is insoluble in dilute ammonia and dissolves in

concentrated ammonia

AgBr (s) + 2NH3(aq) [Ag(NH3)2]+(aq) + Br-

Silver iodide is insoluble in ammonia dilute or concentrated

REACTIONS OF SELECTED HALIDE IONS

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NaCl (s) + H2SO4(l) NaHSO4(s) + HCl (g)

KBr (s) + H2SO4(l) KHSO4(aq) + HBr (g)

2HBr (g) + H2SO4(l) Br2(g) + SO2(g) + 2H2O (g)

KI (s) + H2SO4(l) KHSO4(aq) + HI (g)

2HI (g) + H2SO4(l) I2(g) + SO2(g) + 2H2O(g)

The reactions of concentrated sulphuric acid with solid ionic halides

show that ease of oxidation of halide ion increases in order

Cl-< Br-< I-

REACTIONS OF HALIDE IONS WITH

CONCENTRATED H2SO4

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INDUSTRIAL APPLICATIONS OF HALOGENS AND THEIR

COMPOUNDS

Antiseptics

antiseptics are substances for cleaning injured skin

and preventing bacterial infections

chlorine compounds

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Bleaching agents

oxidising agents . Oxidise coloured compounds colourless

compounds Chlorine used as bleaching agent in the paper and textile industry

Water treatment

chlorine kill harmful bacteria. It is used as a disinfectant for the

purification(sterilisation) of drinking water, in waste water treatmentand in swimming pools

chlorine dissolves in water to form chloric (I) acid

Cl2(g) + H2O(l) HClO (aq) + HCl (aq)

The chlorate (I) ions from chloric (I) acid kill bacteria by oxidisingmolecules on the outer surface of the bacteria, thereby disrupting thestructure of the cells and killing them

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Remaining AgBr isremoved by Na2S2O3

form complex ion

Use developer(hydroquinone),

C6H4(OH)2 to form

negative

Exposing the photographic film tothe light (taking picture)

Developing the film

Fixing the developing film

Photo printing

Black-and-white photographyAgBr light 2Ag+Br2These black silver

crystals form the latent

image