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Page 1

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Shapes of molecules and ions
Demonstrate an understanding of the use of electron-pair repulsion theory to interpret and
predict the shapes of simple molecules and ions
pairs of electrons around the central atom repel each other to a position of maximum
separation and minimum energy
lone pairs have a greater…

Page 2

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Pairs of electrons Shape Bond angle
2 Linear 180
3 Trigonal planar 120
4 Tetrahedral 109.5
5 Trigonal bipyramid 90 and 120
6 Octahedral 90

Apply the electron-pair repulsion theory to predict the shapes of molecules and ions of the above


Discuss the different structures formed by carbon atoms,…

Page 3

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each carbon atom forms four identical bonds to other carbon atoms
tetrahedral arrangement
strong covalent bonds
o very high melting point
o sublimes
o hard; used in drill tips and saws
o good thermal conductor as vibrations travel easily through the stiff lattice
o doesn't conduct electricity because electrons…

Page 4

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Between the extremes of pure ionic and pure covalent bonding there is a range of intermediate
bonds. Polarization of ions leads to distorted ionic bonds. If the polarization is large, the electron
density is distorted so much it will resemble a covalent bond.
if the difference in electronegativity is high,…

Page 5

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Relate the physical properties of materials to the types of intermolecular force present, eg.
The trends in boiling and melting temperatures of alkanes with increasing chain length
o London forces are stronger for larger molecules as they have more electrons
The effect of branching in the carbon chain on the…

Page 6

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Demonstrate an understanding of:
Oxidation number - the rules for assigning oxidation numbers
o elements have an oxidation number of 0
o group 1 and 2 always have an oxidation number of +1 and +2
o hydrogen is always +1, except in hydrides, where it is -1
o oxygen…

Page 7

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Recall the reaction of the elements in group 2 with oxygen, chlorine and water
All react to form solid metal oxides
Reactivity increases down group
Mg (s) + 0.5O2(g)--> MgO (s)

All react to from solid metal chlorides
Mg(s) + Cl2(g) --> MgCl2(s)

Beryllium won't react unless…

Page 8

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Recall the characteristic flame colours formed by group 1 and 2 compounds and explain their
origin in terms of electron transitions
Sodium: yellow (sunny sodium)
Potassium/Caesium: lilac
Lithium/Calcium/Strontium: red
Barium: green (BaG)
Magnesium: colourless

Electrons are given energy and are excited to higher energy levels. However, they fall back down…

Page 9

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- Red-brown gas/liquid (very volatile)
- Partially soluble in water
- Very soluble in a hydrocarbon solvent
- Red-brown solution in both cases
- Grey-black solid
- Sublimes on heating giving a purple gas
- Slightly soluble in water giving a brown solution
- Very soluble in hydrocarbon giving…

Page 10

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- (however, if starch is added too soon, iodine makes an insoluble compound with the
starch and won't react as expected with the thiosulfate)
Evaluation of the results:
- difficult to determine accurately the volume of the liquid in a burette if the meniscus lies
between two graduation marks


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