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How Iodine reacts with metals

Answer Text:
Reaction of halogens with metals.
Reaction of iodine with iron
(ii). Precaution.
- Experiment should be done in a functional fume cupboard or in the open.
Reason:
- Iodine is poisonous and will thus be harmful to the human body.
(iii). Procedure:
- Iodine crystals are heated to generate iodine vapour (fumes).
- The iron wool is then heated and a stream of the iodine gas is passed over heated iron wool as per the diagram.
(iv). Conditions.
Iodine must be heated to generate fumes before heating the iron.
Reason:
So that iodine vapour will drive out air from the boiling tube to prevent oxidation of iron with
oxygen which would otherwise prevent reaction between iron and iodine.
Iron metal must be hot; and this is done by heating.
Reason:
To provide activation energy i.e. the minimum kinetic energy which the reactants must have to form products.
(v). Observations:
- Purple vapour (fumes) of iodine is produced on heating iodine crystals.
- The iron wool glows red-hot upon heating
- The iron wool forms grey black crystals (of iron (II) iodide)
(vi). Reaction equation.
Word: Iron + iodine → Iron (II) iodide.
Chemical: #Fe(s) + I_2(g) → FeI_2(s)#
Grey-black crystals.
Reaction of Iodine with zinc
- Using the same set up bromine also reacts with zinc to form zinc iodide.
Equation: #Zn(s) + I_2(g) → ZnI_2(s).#
Reaction of Iodine with magnesium
- Using the same set up bromine also reacts with zinc to form magnesium iodide.
Equation: #Mg(s) + I_2(g) → MgI_2(s).#
Reaction of Iodine with sodium
- Using the same set up bromine also reacts with zinc to form sodium iodide.
Equation: #2Na(s) + I_2(g) → 2NaI(s).#
Note:
- The reactivity of chlorine with metals is more vigorous than that of bromine, which is more than that of iodine.
- Thus reactivity of halogens with metals decreases down the group.
Reason:
- Halogens react by gaining electrons; the ease of gaining electrons decrease down the group as the atomic size increases which leads to progressive decrease in the force of attraction of electrons in the outermost energy levels by the positively charged nucleus.