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Explain, in terms of electrons, why potassium reacts more violently than sodium. (3 marks)

Explain, in terms of electrons, why potassium reacts more violently than sodium. (3 marks) bigger atom or outer shell electron further from nucleus or more shells (1) less attraction to nucleus or more shielding (1) outer electron more easily lost (1). Group 7 – The halogens. L.O.:

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Explain, in terms of electrons, why potassium reacts more violently than sodium. (3 marks)

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  1. Explain, in terms of electrons, why potassium reacts more violently than sodium. (3 marks) • bigger atom or outer shell electron further from nucleus or more shells (1) • less attraction to nucleus or more shielding (1) • outer electron more easily lost (1)

  2. Group 7 – The halogens L.O.: • Predict the outcome of a reaction between a halogen and halide salts. • Explain the trend in reactivity of group 7 in terms of electronic structure.

  3. Homework: workbook pages 105-107

  4. fluorine F chlorine Cl bromine Br iodine I astatine At Group 7 – the halogens The elements in group 7 of the periodic table, on the right, are called the halogens.

  5. Halogens – what do they look like? Chlorine Bromine Iodine

  6. When iodine is heated gently, it changes directly from a solid to a gas without first becoming a liquid. This is called sublimation. Halogen vapours Bromine and iodine are not gaseous, but have low boiling points. This means that they produce vapour at relatively low temperature. They are volatile. Bromine produces some red-brown vapour, seen here above the liquid bromine in the jar.

  7. decrease in reactivity How does electron structure affect reactivity? The reactivity of alkali metals decreases going down the group. What is the reason for this? • The atoms of each element get larger going down the group. F • This means that the outer shell gets further away from the nucleus and is shielded by more electron shells. Cl • The further the outer shell is from the positive attraction of the nucleus, the harder it is to attract another electron to complete the outer shell. • This is why the reactivity of the halogens decreases going down group 7.

  8. F F + F F  How do halogen molecules exist? All halogen atoms require one more electron to obtain a full outer shell and become stable. Each atom can achieve this by sharing one electron with another atom to form a single covalent bond. This means that all halogens exist as diatomicmolecules:F2, Cl2, Br2 and I2.

  9. fluorine F chlorine Cl bromine Br iodine I astatine At Reactions of the group 7 elements

  10. KBr + Cl2 clip

  11. Displacement Equations Potassium Bromide and Chlorine: • 2KBr + Cl2 2KCl + Br2 Potassium Iodide and Chlorine: • 2KI + Cl2  2KCl + I2 Potassium Iodide and Bromine: • 2KI + Br2 2KBr + I2

  12. salt (aq) potassiumchloride potassiumbromide potassiumiodide halogen chlorine 2KCl + Br2 2KCl + I2 bromine no reaction 2KBr + I2 iodine no reaction no reaction Displacement reactions: summary The reactions between solutions of halogens and metal halides (salts) can be summarised in a table:

  13. Q1) What is the product of the reaction between iron and iodine? Q2) Which gas is more reactive, chlorine or iodine?

  14. Tasks: • Workbook page 108. • Halogens worksheet.

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