8.2 The Halogens
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Halogens are diatomic, but in what form are they found naturally?
halide ions within stable compounds
What properties of halogens change down the group?
BOILING POINT ￪ ELECTRONEGATIVITY ￬ REACTIVITY / OXIDISING POWER ￬
Why does the boiling point of halogens increase down the group?
more electrons stronger induced dipoles/London forces more energy required to overcome intermolecular forces
Why does the electronegativity of halogens decrease down the group?
more shells more shielding weaker electrostatic attraction between shared pair + nucleus (despite increased nuclear charge)
Why does the reactivity/oxisiding power of halogens decrease down the group?
halogens react/act as oxidising agents by gaining electrons: • more shells • greater shielding • weaker electrostatic attraction of electrons to nucleus • electrons gained less easily
Why are halogens a good oxidising agent?
ability to accept electrons
What colour is chlorine in water?
pale green
What colour is chlorine in cyclohexane?
pale green
What colour is bromine in water?
orange
What colour is bromine in cyclohexane?
orange
What colour is iodine in water?
brown
What colour is iodine in cyclohexane?
violet
What happens when cyclohexane is added to non-polar halogen molecules?
halogens dissolve more readily in cyclohexane than water may be a colour change
What type of solvent is cyclohexane?
non-polar, organic
Why do halogens dissolve more readily in cyclohexane than in water?
cyclohexane is non-polar + so are halogens so more/stronger intermolecular force interactions
Why is cyclohexane sometimes added to aqueous solutions of bromine and iodine?
to differentiate between them (bromine + iodine in water = brown/orange + cyclohexane, bromine = brown, iodine = violet)
What is disproportionation?
REDOX reaction in which the SAME ELEMENT is both OXIDISED + REDUCED
Cl2 (aq) + H2O (l) ⟶
HClO (aq) + HCl (aq)
Cl2 (aq) + 2NaOH (aq) ⟶
HClO (aq) + NaCl (aq) + H2O (l)
What is the formula for bleach?
HClO
Under what conditions is bleach formed?
COLD, DILUTE aqueous SODIUM HYDROXIDE
What is the danger of chlorine gas?
toxic, respiratory irritant
Chlorine in drinking water can react with organic hydrocarbons (from decaying vegetation) to form…
chlorinated hydrocarbons which are carcinogens
What is 1 advantage + 1 disadvantage of using bleach in water treatment?
Advantages - kills bacteria/sterilises Disadvantages - toxic, could form chlorinated hydrocarbons