Group 7

• The atomic radius of group 7 elements​ increases down the group​ due to additional electron shells.
• Halogen atoms have high electronegativities, so they readily form negative ions by gaining an electron.
• Group 7 elements have high boiling points because they form strong intermolecular forces (dipole-dipole interactions).
• The group 7 elements are highly reactive non-metals that need to gain an electron to form a 1- ion and achieve a full outer shell of electrons.
• The atomic radius of group 7 elements increases down the group due to additional electron shells.
• The group 7 elements need to gain an electron as atomic radius increases, making it harder to attract an electron and therefore reactivity decreases down the group.
• The first ionisation energy of group II metals decreases down the group due to a greater atomic radius and increased amounts of shielding.
• The group 7 elements are simple covalent molecules held together with van der waals forces, and the strength of these intermolecular forces increases as the Ar of the molecule increases, resulting in a higher boiling point.
• Fluorine is a gas at room temperature whereas iodine is a solid.
• The halogens act as good oxidising agents as they accept electrons from the species being oxidised and are reduced, with this oxidising power decreasing down the group as their ability to attract electrons decreases due to shielding and a greater atomic radius.
• A halogen will displace any halide beneath it in the Periodic Table due to its relative oxidising strengths.
• The negative ions of halogens are known as halide ions, which are good reducing agents as they donate electrons to the species being reduced and are themselves oxidised, with this reducing power increasing down the group as electrons are easier to lose from larger ions due to shielding and a larger atomic radius.
• Acidified silver nitrate is used to test for halide ions as it reacts to form different coloured precipitates depending on the ion present, and these precipitates may not be clear to distinguish so they can be tested further using ammonia.
• If ammonium ions are present, ammonia gas is given off, which is a base, and the presence of ammonium ions can be tested by holding red litmus over a petri dish of the substance being tested, it will turn blue if ammonium ions are present.
• Anions such as Halides, Sulfate (SO 4 2- ), Hydroxide (OH - ), and Carbonate (CO 3 2- ) are tested for using acidified silver nitrate and ammonia.
• When an acid such as HCl is added to a substance containing Carbonate (CO 3 2- ), the substance will fizz (effervescence) and CO 2 gas is given off, which can be collected and bubbled through limewater to confirm it as carbon dioxide.
• Alternatively, ammonium ions can be tested for in the same way but by adding NaOH to produce the ammonia gas faster.
• Chlorine reacts with cold water to produce Chlorate(I) ions (ClO - ) and chloride ions, in a disproportionation reaction where the chlorine is both oxidised and reduced.
• Chlorine can be mixed with cold, aqueous sodium hydroxide to produce sodium hypochlorite, a key ingredient in the production of bleach.
• Anions like Halides can be identified with red litmus, which turns blue, or using universal indicator, which turns blue-purple.
• Anions like Sulfate (SO 4 2- ) can be identified with BaCl 2 which reacts to form a white precipitate.
• In the presence of UV light, chlorine decomposes water to produce oxygen and hydrochloric acid, reducing the chlorine in the process.
• Chlorine is used in small quantities to kill bacteria in water treatment processes, posing some risks as chlorine can be toxic.
• What are the 5 halogens?

  Fluorine, Chlorine, Bromine, Iodine & Astatine
• Why isn't astatine studied?

  Because it's very radioactive and can't exist for more than a few seconds before decaying.
• What oxidation state are the G7 elements usually found in?

  -1, found as X-1 ions (known as halide ions)
• Appearance of G7 elements: Fluorine

  Very pale yellow gas, highly reactive
• Appearance of G7 elements: Chlorine

  Pale green gas, poisonous in high concentrations
• Appearance of G7 elements: Bromine

  Red liquid, gives off dense brown or orange poisonous fumes
• Appearance of G7 elements: Iodine

  Shiny grey solid that sublimes to a purple gas
• Appearance of G7 elements: Astatine

  Black solid, is radioactive
• Trends of G7: Boiling point as you go down the group

  Increases-Number of VDW forces increase between molecules as they're larger-More energy is needed to break the bonds
• Trends of G7: Electronegativity

  Decreases-Atomic radius increases-Shielding increases-Less attraction between the outer electrons and the protons in the nucleus
• Are the halogens oxidising or reducing agents?

  Oxidising-They can accept electrons and are reducedF2(g) + 2e- --> 2F-(aq)Cl2(g) + 2e- --> 2Cl-(aq)Br2(l) + 2e- --> 2Br-(aq)I2(aq) + 2e- --> 2I-(aq)
• Trends of G7: Oxidising power

  Decrease-Atoms become larger-Shielding increases-Outer e-'s are less attracted to the nucleus
• Are halides oxidising or reducing agents?

  Reducing-They can lose electrons and can get oxidised2F-(aq) --> F2(g) + 2e-2Cl-(aq) --> Cl2(g) + 2e-2Br-(aq) --> Br2(l) + 2e-2I-(aq) --> I2(aq) + 2e-
• Trends of G7: Reducing power

  Increase-Atoms larger-Shielding increases-Electrons aren't attracted to the nucleus as strongly so they're more easily lost
• Trends of G7: Displacement reactions

  The more reactive halogens (strongest oxidising agents) will displace the more reactive halides (strongest reducing agents) from solutions of their ions
• What happens when: potassium chloride reacts with chlorine?

  No reaction
• What happens when: potassium chloride reacts with bromine?

  No reaction