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The Halogens

The Halogens. C omplete this table. Can you explain the trend in boiling point?. The Halogens. C omplete this table. Can you explain the trend in boiling point?. Temporary dipole occurs in one molecule owing to an unequal distribution of the electron cloud around it.

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The Halogens

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  1. The Halogens Complete this table. Can you explain the trend in boiling point?

  2. The Halogens Complete this table. Can you explain the trend in boiling point?

  3. Temporary dipole occurs in one molecule owing to an unequal distribution of the electron cloud around it. This temporary dipole induces a dipole in another molecule and the two attract each other. Known as induced dipole-dipole forces or Van der Waals forces. Explaining the trend in boiling point

  4. The strength of van der waals forces increase: The larger the molecule (due to a larger electron cloud)

  5. salt (aq) potassiumchloride potassiumbromide potassiumiodide halogen chlorine 2KCl + Br2 2KCl + I2 bromine no reaction 2KBr + I2 iodine no reaction no reaction DISPLACEMENT REACTIONS

  6. The Halogens: Recognising them • The halogens form solutions with different colours. A colour change will show if a reaction has taken place. If you shake the reaction mixture with an organic solvent it can help distinguish between them

  7. What is the trend in reactivity of the halogens?How can we explain this trend?

  8. The halogens get less reactive as we descend the group.This is because…- atomic size- shielding- nuclear attractionHow does this link to redox?

  9. Displacement: a redox reactionWrite an equation for the reaction between chlorine and bromide ions, showing the changes in oxidation numbers. Which species is the oxidising agent?

  10. Cl2 (aq) + 2Br- (aq)  2Cl- (aq) + Br2 (aq)0 -1 -1 0 Chlorine is reduced Bromine is oxidised Chlorine acts as an oxidising agent

  11. TRENDS IN OXIDISING ABILITYHalogens react by gaining electrons This means they are oxidising agents They themselves are reduced Cl2 + 2e- 2Cl- Gain of electrons O xidationI sL osingR eductionI sG aining Oxidising ability of halogens decreases down the group Because atoms become larger (and less electronegative)

  12. Br I Cl Oxidising power trend: Cl2 > Br2 > I2 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)

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