11.0 The Halogens

1. 11.0 The Halogens Text book p166 to 173

2. AQA AS Specification

3. Halogens What are the Halogens, what does their name mean, and where are they found in the Periodic Table? • The Halogens are elements that are found in Group 7 (VII) of the PT. The name means “salt former”. Name some compounds that contain a halogen What is the valency (OXIDATION NUMBER) of the halogens?

4. Appearance fluorine video Fluorine, F2, is a pale yellow gas at room temperature.

5. Chlorine video Chlorine, Cl2, is a pale green gas at room temperature.

6. Bromine video Bromine, Br2, is a dark red liquid at room temperature. It is the only liquid non-metal.

7. Bromine is volatile and readily forms a dark red vapour.

8. iodine video Iodine, I2, forms shiny black crystals at room temperature.

9. When warmed, iodine crystals sublime (turn directly to a gas), forming a purple vapour.

10. Fluorine What is unusual about the bonding in fluorine molecule? Explain. • Compared to the other halogens, the F-F bond is very weak. • This is because the fluorine atoms are very small and there is a lot of repulsion between the bonding electrons. Summarize the physical trends in Group VII, draw stick graphs for the data and explain the trends.

11. Atomic Radius The atomic radius increases down Group 7. Going down the group, there are more filled energy levels between the nucleus and the outer electrons. This results in the outer electrons being shielded more from the attraction of the nucleus.

12. Boiling point The boiling point increases down Group 7. The strength of the instantaneous dipole−induced dipole forces between the molecules increases as the size of the molecules increases.

13. Electronegativity Electronegativity decreases down Group 7. Fluorine is the most electronegative element in the periodic table. The atomic radius increases, the outer electrons are more shielded, so bonding electrons are less strongly attracted to the nucleus. (Fig 2 p167)

14. 11.2 Chemical reactions of the Halogens P 168 ( Lister) P138 (Atkinson)

15. Oxidation ability Oxidation is the loss of electrons. What is Oxidation? An oxidizing agent is an electronacceptor, the agent is reduced during the course of the reaction. This forms a redox reaction. What is an oxidizing agent?

16. Oxidising power trend: Cl2 > Br2 > I2 Br I Cl When a halogen acts as an oxidising agent, it gains electrons (taken from the oxidised species). X2 + 2 e-→ 2 X- Going down the group it becomes harder to gain an electron because: atoms are larger & there is more shielding (due to extra electron shell)

17. Task: • Read p 168 (Lister) and complete the table • React each Potassium Halide with each halogen water. • Note down the colour change (if there is any) • Write the ionic equation for the displacement. • Check you are correct by reading page 168

26. HSW – Extraction of Bromine homework • Create a presentation on the extraction and uses of Bromine and of Iodine. • Use the material in the text book (page 169) and from the internet. • Your presentation could be as a poster or as a powerpoint. • Maximum of 6 slides.

27. 11.3 Reactions of halide ions

28. Reducing agents Reduction is the gain of electrons What is reduction? What happens when a Halide is used as a reducing agent? Give the half equation for the reaction 2 X–→X2 + 2 e– When a halide ion reduces another substance, the halide is oxidised to a halogen.

29. Experiment This experiment compares how well the halides reduce H2SO4 to compare the reducing power of the halide ions. Some of the products are very toxic – hence the video clips! Watch the clips and complete the OBSERVATIONS column in the table NaCl + sulphuric acid NaBr + Sulphuric acid NaI + sulphuric acid

32. Formation of hydrogen halides: NaX + H2SO4 → NaHSO4 + HX e.g. NaCl + H2SO4 → NaHSO4 + HCl Complete the final two columns of the table.

34. 2 Cl–→ Cl2 + 2 e– 2 Br–→ Br2 + 2 e– 2 I–→ I2 + 2 e– H2SO4 + 2 H+ + 2 e–→ SO2 + 2 H2O H2SO4 + 6 H+ + 6 e–→ S + 4 H2O H2SO4 + 8 H+ + 8 e–→ H2S + 4 H2O Write half equations for: Cl–→ Cl2 Br–→ Br2 I–→ I2 H2SO4 → SO2 H2SO4 → S H2SO4 → H2S

39. Reducing power trend Cl– does not reduce H2SO4 Br– reduces H2SO4 from S(+6) to S(+4) I– reduces H2SO4 from S(+6) to S(-2)

40. Reducing power trend: Cl– < Br– < I– Cl– Br– I– When a halide ion acts as a reducing agent, it loses electrons (given to the reduced species). 2 X–→ X2 + 2 e– Down the group it becomes easier to lose an electron because: ions are larger & there is more shielding (due to extra electron shell)

41. Identification of metal halides Complete practical ES4.4, or N-ch2-06