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.
Group 7 worksheet.
Use broadworks animation (Cl2 + KBr or clip)
Halogens react with iron (clipbank)

3. Homework: workbook pages 105-107

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

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

6. 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.
Photo credit: Dr John Mileham
Bromine produces some red-brown vapour, seen here above the liquid bromine in the jar.
When iodine is heated gently, it changes directly from a solid to a gas without first becoming a liquid.
This is called sublimation.

7. 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
decrease in reactivity
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. 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. +  F
This means that all halogens exist as diatomic molecules: F2, Cl2, Br2 and I2.

9. Reactions of the group 7 elementsBr Cl F At
fluorine
chlorine
bromine
iodine
astatine

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

13. Q1) What is the product of the reaction between iron and iodine
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.