1. All toxic All form Diatomic molecules All form ionic salts
Halogens
Group VII
All toxic
All form Diatomic molecules
All form ionic salts

2. How does the trend
in atomic radius
dictate:
(i) The trend in boiling
points?

3. Boiling points of Halogens

4. Boiling points of Halogens

5. How does the trend
in atomic radius
dictate:
(ii) The ability of the
halogens to act as an oxidising agent?

6. GROUP 7 : THE HALOGENS Halogen Symbol Formula State at 298K Colour
Fluorine
Chlorine
Bromine
Iodine
Astatine F Cl Br I At F2
Cl2
Br2 I2
At2
Gas
Liquid
Solid
Pale yellow
Green
Dark red
Dark grey
Black

8. Fluorine F [He]2s22p5
Chlorine Cl [Ne]3s23p5
Bromine Br [Ar]3d104s2 4p5
Iodine I [Kr]4d105s2 5p5
Astatine At [Xe]4f14 5d106s2 6p5

9. Halogens are powerful oxidising agents
All halogens gain electrons to make halide ions, so all the halogens are oxidising agents. You need to know the trend in the oxidising power as you go down group VII.
Chlorine atoms gain an electron to make chloride ions:
Cl2 + e- g 2Cl-
The chlorine atom has gained an electron so is reduced, so the chlorine atom is an oxidising agent (oxidising agents are electron acceptors).

10. Down the group the halogens become weaker oxidising agents
Down the group the halogens become weaker oxidising agents. Also the halide ions become stronger reducing agents.

11. Cl2(g) + 2KBr(aq) g Br2(aq) + 2KCl(aq)+1 -1 +1 -1
Cl2(g) KBr(aq) g Br2(aq) KCl(aq)
Green
gas
Colourless
solution
Red-brown
solution
Colourless
solution
Write in the oxidation numbers to show what is being oxidised and reduced.
Chlorine is being reduced (and is the oxidising agent)
Also what are the oxidation and reducing agents?
Bromine is being oxidised (and is the reducing agent)
Br2(l) KCl(aq) g No reaction

13. HALOGENS - DISPLACEMENT REACTIONS
KCl(aq)
KBr(aq)
KI(aq)
Cl2(aq)
No Reaction
Pale Green Solution
Cl2(aq) + 2Br-(aq)g 2Cl-(aq) + Br2(aq)
Orange Solution
Cl2(aq) + 2I-(aq)g 2Cl-(aq) + I2(aq)
Brown Solution
Br2(aq)
Br2(aq) + 2I-(aq)g 2Br-(aq) + I2(aq)
I2(aq)

14. Aqueous halogens in cyclohexane
Halogens are non-polar molecules. They will therefore dissolve best in non-polar solvents, like cyclohexane.
Cyclohexane will not mix with water so two distinct layers will form.
Cyclohexane
layer
Aqueous
layer
Cl2(aq)
Br2(aq)
I2(aq)

15. Bromine water (aqueous bromine, Br2) is shaken with a volume of cyclohexane, and then the follow aqueous solutions are added to separate portions.
a) Aqueous sodium iodide
b) Aqueous chloride
c) Aqueous sodium astatide
The orange cyclohexane layer would turn purple
Br2(aq) + 2I-(aq) g 2Br-(aq) + I2(aq)
No change
Given its position in group VII, we would expect astatine to be darker in colour than iodine . The orange cyclohexane layer would turn this colour.
Br2(aq) + 2At-(aq) g 2Br-(aq) + At2(aq)
Each mixture is shaken again. Describe what you would expect to see. Write equations for any reactions that would occur.

16. Cl2(aq) + H2O(l) g HCl(aq) + HClO(aq)
When chlorine reacts with water a mixture of hydrochloric acid (HCl) and chloric (I) acid (HClO) is formed
Cl2(aq) + H2O(l) g HCl(aq) + HClO(aq)
Use oxidation numbers to deduce what atom is being oxidised and what is being reduced.
The reaction is a dispropotionation because chlorine is both oxidised and reduced

17. Reaction of chlorine with aqueous sodium hydroxide
Cl2(aq) + 2NaOH(aq) g NaCl(aq) + NaClO(aq) + H2O(l)
NaClO is sodium chlorate (I), also called sodium hypochlorite. A dilute sodium chlorate (I) is a key ingredient of chlorine-based household bleaches.

18. Bromine reacts with cold dilute alkali to give a colourless solution containing Br- and BrO- ions.
Write a balanced chemical equation for this reaction
What are the oxidation states of bromine before and after the reaction
c) Name this type of reaction.
Br2 + 2NaOH g NaBr NaOBr H2O
0 before, -1 and +1 after
disproportionation

19. TESTING FOR HALIDES – AgNO3
• make a solution of the halide
• acidify with dilute nitric acid - prevents the precipitation of other salts
• add a few drops of silver nitrate solution
• treat any precipitate with dilute ammonia solution
• if a precipitate still exists, add concentrated ammonia solution

20. TESTING FOR HALIDES – AgNO3
CHLORIDE white ppt of AgCl soluble in dilute ammonia
BROMIDE cream ppt of AgBr insoluble in dilute ammonia but soluble in conc.
IODIDE yellow ppt of AgI insoluble in dilute and
conc. ammonia solution

21. TESTING FOR HALIDES – AgNO3
CHLORIDE white ppt of AgCl soluble in dilute ammonia
BROMIDE cream ppt of AgBr insoluble in dilute ammonia but soluble in conc.
IODIDE yellow ppt of AgI insoluble in dilute and
conc. ammonia solution
halides precipitate as follows Ag+(aq) + X¯(aq) ——> Ag+X¯(s)
when they dissolve in ammonia a colourless diammine complex is formed [Ag(NH3)2]+(aq)

22. TESTING FOR HALIDES – AgNO3
CHLORIDE
BROMIDE
IODIDE
PLACE A SOLUTION OF THE HALIDE IN A TEST TUBE

23. TESTING FOR HALIDES – AgNO3 ADD SOME DILUTE NITRIC ACID
CHLORIDE
BROMIDE
IODIDE
ADD SOME DILUTE NITRIC ACID

24. TESTING FOR HALIDES – AgNO3 ADD SILVER NITRATE SOLUTION
CHLORIDE
BROMIDE
IODIDE
ADD SILVER NITRATE SOLUTION
WHITE PRECIPITATE OF SILVER CHLORIDE AgCl
CREAM PRECIPITATE OF SILVER BROMIDE AgBr
YELLOW PRECIPITATE OF SILVER IODIDE AgI

25. TESTING FOR HALIDES – AgNO3 ADD DILUTE AMMONIA SOLUTION
CHLORIDE
BROMIDE
IODIDE
ADD DILUTE AMMONIA SOLUTION
WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE
CREAM PRECIPITATE OF SILVER BROMIDE - INSOLUBLE
YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE

26. TESTING FOR HALIDES – AgNO3 ADD CONCENTRATED AMMONIA SOLUTION
CHLORIDE
BROMIDE
IODIDE
ADD CONCENTRATED AMMONIA SOLUTION
WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE
CREAM PRECIPITATE OF SILVER BROMIDE - SOLUBLE
YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE

28. a) What would you expect to be the physical state of astatine at room temperature. Explain your answer
b) Fluorine and chlorine both react with sodium metal to form a salt.
i) Write a balanced equation for each reaction
ii) Which of the two reaction will be most vigorous. Why?
iii) What structure and bonding will the products have?
c) What is the oxidation number of chlorine in Cl2, CaCl2, Cl2O7 and ClO2?
Solid. At2 molecules are larger than I2 molecules (At2 molecules have more elctrons than I2 molecules) therefore van der Waals’ forces will be stronger. Iodine is a solid at room temperature, therefore so is astatine
Cl2 + 2Na g 2NaCl
F2 + 2Na g 2NaF
The fluorine reaction. Fluorine is more reactive than chlorine as it has a smaller atomic radius. This means it is easier for an incoming electron to enter its outer shell as it has experiences less shielding and is closer to the nucleus.
Both are giant ionic
0, , +7,

29. 203.3 g
White precipitate/goes white

30. Ag+(aq) + Cl-(aq) g AgCl(s)
AgCl dissolves in NH3(aq)
AgBr dissolves in conc NH3(aq)/partially soluble in NH3(aq)
AgI insoluble in NH3(aq) or conc NH3(aq)
White precipitate/goes white