AQA AS Chemistry Unit 2: Group 7 The Halogens

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Chemistry Unit 2: Group 7 The Halogens

  • Halogen has 7 electrons in its highest energy level, reacts to gain electron and causes the loss of electron so is a oxidising agent

  • Halide has full highest energy level, reacts to lose electron and causes the gain of electron so is a reducing agent

The Halogens

  • Down the group atomic radius increases, boiling point increases due to bigger Van der Waals due to more electrons meaning element has larger temporary dipoles and the electro-negativity decreases as the larger the atom so the more electrons in energy levels meaning more shielding

  • Chemical Trend: Halogens have high oxidising power so cause oxidation. They themselves are reduced so gain an electron to have a full energy level

  • Down the group oxidation power decreases since more shielding from the nucleus and there is more distance from the nucleus

Chemical Reactions of the Halogens

  • The oxidising ability of the halogens increases up the group


Displacement Reactions

  • Halogens react with metal halides to displace them (If the halogen ismore reactive)

  • The halides are colourless solutions

  • Fluorine oxidises Chloride,Bromide and Iodide (Cl2 is faint yellow, Br2 is orange, I2 is red)

  • Chlorine oxidises Bromide and Iodide (Br2 is yellow, I2 is orange/brown)

  • Bromine oxidises Iodide (red/brown)

  • Fluorine cannot be tested in an aqueous solution as it reacts with water

Reactions of Halide Ions

  • Halides can lose their extra electrons

  • They act as reducing agents

  • Reducing power increases down the group as:

  • Larger atomic radius

  • Less attraction between nucleus and highest energy level

  • Due to increased distance there is more shielding

Sodium Chloride and Concentrated Sulfuric Acid

  • Chloride: White steamy fumes of hydrogen chloride, solid sodium hydrogensulfate formed

  • Isn't a redox reaction as there is no oxidation state change it is a acid-base reaction

  • The chloride ion is too weak a reducing agent to reduce the Sulfur

  • NaCl(s) + H2SO4(l) -> NaHSO4(s) + HCl(g)

  • Similar reaction with sodium fluorine as the fluorine ion is an even weaker reducing agent

Sodium Bromide and Concentrated Sulfuric Acid

  • Steamy white fumes of hydrogen bromide formed

  • Brown fumes of bromine and colourless Sulfur dioxide formed


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