Can you draw Bohr diagrams for flourine and chlorine onto your worksheet?
Can you draw Bohr diagrams for flourine and chlorine onto your
worksheet?
Group 7 – the halogensThe elements in group 7 of the periodic table, on the right, are called the halogens.
fluorine
chlorine
bromine
iodine
astatine
I
Br
Cl
F
At
Halogens – what do they look like?
Chlorine Bromine
Iodine
Halogen vapoursBromine 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.
When iodine is heated gently, it changes directly from a solid to a gas without first becoming a liquid.
This is called sublimation.
How does electron structure affect reactivity?The reactivity of halogens decreases going down the group. What is the reason for this?
The atoms of each element get larger going down the group.
This means that the outer shell gets further away from the nucleus and is shielded by more electron shells.
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.
decr
ease
in re
activ
ity
F
Cl
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 diatomic molecules:F2, Cl2, Br2 and I2.
+ F F F F
Halogens in competition
Chlorine is more reactive than iodine or bromine. It can “push” (displace) bromine or iodine out of solution.
Cl2(aq) + 2KBr(aq) 2KCl(aq) + Br2(aq)
Halogens in competition
Chlorine is more reactive than iodine or bromine. It can “push” (displace) bromine or iodine out of solution.
Cl2(aq) + 2KBr(aq) 2KCl(aq) + Br2(aq)
Let’s have a look at some demonstrations of halogens
Starter
• As a group you have 5 min to ‘act out’ a displacement reaction of a halogen and it’s corresponding halide.
• Bonus points for using actual names of the elements/chemicals involved
Halogens in competition
Chlorine is more reactive than iodine or bromine. It can “push” (displace) bromine or iodine out of solution.
Cl2(aq) + 2KBr(aq) 2KCl(aq) + Br2(aq)
Halogens in competition
Chlorine is more reactive than iodine or bromine. It can “push” (displace) bromine or iodine out of solution.
Cl2(aq) + 2KBr(aq) 2KCl(aq) + Br2(aq)
Tasks for this lesson:1. Carry out the practical detailed on your
‘Reactions of the halogens’ sheet (1 per group)
2. On a separate sheet try and write word AND chemical equations for the displacement reactions that DID occur
3. As an extension try and BALANCE the equations
Displacement reactions: summaryThe 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) potassiumchloride
potassiumiodide
potassiumbromide
2KCl + Br2
no reactionno reaction
no reaction
Displacement EquationsPotassium Bromide and Chlorine:• 2KBr + Cl2 2KCl + Br2
Potassium Iodide and Chlorine:• 2KI + Cl2 2KCl + I2
Potassium Iodide and Bromine:• 2KI + Br2 2KBr + I2