pblock elements: Halogens

1
p-block elements Halogens
Chemists get to know chemicals just as people
know their friends.
2
p-block elements Halogens

• Characteristic properties of the halogens
• Variation in properties of the halogens
• Variation in chemical properties of the halogens
• Comparative study of the reaction of X-
• Anomalous behaviour of HF (forming HF2- and
  ability to react with glass)
• Uses of halogen and halogen containing compounds
  telfon / fluoridate drinking water Na2SiF6 /
  disinfectant / films coating / iodine tincture /
  prevent goitre /medical diagnosis in thyroid
  gland )

3
p-block elements Halogens
Characteristic properties of the halogens High
E.N. / High E.A. / Max. oxidation state is 7
(except F) / coloured /
Br2
Cl2
FHe2s22p5 ClNe3s23p5 BrAr3d104s24p5 IKr
4d105s25p5
I2
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p-block elements Halogens
Variation in properties of the halogens m.p. /
E.N. / E.A. / Bond enthalpy In general, atomic
size increases (m.p. increases), screening effect
increases, nuclear attraction decreases (E.N.
decreases). Small size in F, repulsion among lone
pair electrons is large(bond enthalpy of F F
small) and repulsion among incoming electron and
electrons in F is large (E.A. is less negative).
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p-block elements Halogens
Variation in properties of the halogens m.p. /
E.N. / E.A. / Bond enthalpy
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p-block elements Halogens

• Variation in chemical properties of the halogens
• Oxidizing power decreases down the group.
• (due to decreasing E.N. and E.A.)
• Reactions with Na, Fe2, P and Xe
• 2Na X2 ? 2NaX
• 2Fe2 X2 ? 2Fe3 2X-
• 2P 3X2 ? 2PX3 (X I)/ 2P 5X2 ? 2PX5(X F)
• Xe F2 ? XeF2

Na react with Cl2
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p-block elements Halogens

• Variation in chemical properties of the halogens
• All halogens (except F2) disproportionate in
  alkalis.
• Reactions with NaOH
• Cold F2 2NaOH ? NaF OF2 H2O
• Hot F2 4NaOH ? 4NaF O2 2H2O (OF2 decompose
  when hot)
• Cold X2 2NaOH ? NaX NaOX H2O
• Hot 3X2 6NaOH ? 5NaX NaXO3 3H2O

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p-block elements Halogens

• Comparative study of the reaction of X-
• Reactions with
• Halogens
• F2 2Cl- ? 2F- Cl2 but Cl2 2F- ? No
  reaction
• H2SO4(conc.)
• NaF H2SO4 ? HF NaHSO4 but
• 8NaI 9H2SO4 ? 4I2 8NaHSO4 H2S 4H2O
• 3. H3PO4 3NaX 3H3PO4 ? 3HX Na3PO4

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p-block elements Halogens
Comparative study of the reaction of X- Reactions
withH2SO4(conc.)
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p-block elements Halogens
Comparative study of the reaction of X- Reactions
with 4. AgNO3 / H3O Ag X- ? AgX(s) (H3O
eliminate OH-, CO32- or SO32- which will
interfere the result by the formation of Ag2O or
Ag2CO3 or Ag2SO3.)
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p-block elements Halogens
Comparative study of the reaction of X- Reactions
with AgNO3 / H3O Ag X- ? AgX(s)
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p-block elements Halogens

• Comparative study of the reaction of X-
• Reactions of AgX with
• NH3(excess)
• AgCl(s) 2NH3(aq) ? Ag(NH3)2(aq) Cl-(aq)
• 2. light
• 2AgCl(s) ? 2Ag(s) Cl2(g)
• 2AgBr(s) ? 2Ag(s) Br2(g)

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p-block elements Halogens
Comparative study of the reaction of X-
Reactions of AgX with light 2AgBr(s) ? 2Ag(s)
Br2(g)
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p-block elements Halogens
Uses of halogen and halogen containing compounds
telfon / fluoridate drinking water Na2SiF6 /
disinfectant / films coating / iodine tincture /
prevent goitre /medical diagnosis in thyroid
gland )
X-ray photo of the digestive system of a patient
who has taken a barium meal