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Physical properties of halogens
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Electronic configurations
• Halogens are in group VII of the periodic table and so have seven electrons in their outer shell.
• F 1s2 2s2 2p5• Cl 1s2 2s2 2p5 3s2 3p5• Br 1s2 2s2 2p5 3s2 3p5 4s2 (3d10) 4p5• I 1s2 2s2 2p5 3s2 3p5 4s2 (3d10) 4p5 5s2 (4d10) 5p5
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Bonding• Halogens require one electron to
complete their outer shell.
• This can be obtained by gaining an electron to form a halide anion.
• Eg: Cl + e- → Cl-
• Alternatively they can share electrons in a single covalent bond;
•Clx + Hx → ClxxH
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Diatomic molecules
• The halogens are found in their native states as diatomic molecules.
• F:F
• Cl:Cl
• Br:Br
• I:I• Halogens form simple molecular lattices held
together by weak van der Waals forces.
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Chlorine is a pale green gas at room temp and pressure.
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Bromine is an orange brown liquid at room temp and pressure.
It has a low BP and is highly volatile.
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Iodine is a grey, silvery solid at room temperature and pressure.
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Iodine will not melt, on heating it sublimes, forming a purple gas.
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MPs and BPs
MP (oC) BP (oC)
F -220 -188
Cl -101 -35
Br -7 59
I 113
Plot the MPs and BPs and explain the trend in terms of structure/bonding.
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MPs and BPs of halogens
• The MPs and BPs increase down the group.
• This is because there are more electrons in the atoms.
• Which means that the van der Waals forces between molecules become stronger.
• So more energy is required to break them and melt or boil the sample.
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Solubility of halogens
Organic layer non-polar solvent.
Aqueous layer polar
solvent
Halogens are more soluble in non-polar than in polar
solvents.
The bond between
atoms is not polarised.
Bromine water shaken with hexane.
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Chlorine is more soluble in organic
solvents.
Aqueous layer
Chlorine is not very soluble in
water, but reacts to form pale
green chlorine water.
Solubility of chlorine
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Solubility of bromine
Bromine readily dissolves in
water to give an orange brown
solution.
Bromine is more soluble in organic
solvents.
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Solubility of iodine
Iodine is not very soluble in water.
But it is much more soluble in
KI, giving a yellow brown solution.
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Iodine is much more soluble in
organic solvents.
Aqueous layer
Organic layer