1. Structure

2. Magnesium has metallic bonding.
(i)Draw a diagram to show what is meant by metallic bonding. Label the diagram.
[2]
(ii) Why is magnesium a good conductor of electricity?
[1]

3. (i)
positive ions/cations and negative electrons
Can be described in words only for both marks 2
(ii) contain free/mobile/delocalised electrons 1

6. Draw a dot-cross diagram for sodium chloride
Draw how you think the ions are arranged in
solid sodium chloride.
Sodium chloride has a high melting point. Explain
Draw what you think happens when sodium chloride
dissolves in water
What is needed for a substance to be able to
conduct electricity?
Explain why solid sodium chloride doesn’t conduct when
solid but does when molten or in solution.

7. Draw a dot-cross diagram for sodium chloride
Draw how you think the ions are arranged in
solid sodium chloride.
Sodium chloride has a high melting point. Explain
Draw what you think happens when sodium chloride
dissolves in water
What is needed for a substance to be able to
conduct electricity?
Explain why solid sodium chloride doesn’t conduct when
solid but does when molten or in solution.

8. Sodium Chloride - an Ionic Crystal

9. What you need to know: Sodium chloride is an ionic lattice.
Each chloride ion is surrounded by six sodium ions. And vice versa.
The ions are held together by strong electrostatic forces which require much energy to break. Therefore NaCl has a high melting point.

10. You must be able to draw NaCl – at least:
The bonding is ionic.

11. Will ionic compounds conduct electricity when solid?
No – the ions are fixed in position.
When molten or in solution the ions become free to move so NaCl will then conduct electricity

12. Solubility Ionic compunds only dissolve in polar solvents like water.
Use p 69 in your text book to help you explain why. Draw a diagram in your answer.

14. Diamond - A giant covalent crystal

15. Diamond is the hardest known natural material and one of the two best known forms (or allotropes) of carbon, whose hardness and high dispersion of light make it useful for industrial applications and jewellery.

16. Draw a dot cross diagram to show how 1 C atom
can covalently bond to 4 other C atoms.
What will the shape be?
What will you expect the melting point to be?
Why?
What will you expect the solubility in water to be?
Why?
What will you expect the electrical conductivity to be?
Why?

17. Draw a dot cross diagram to show how 1 C atom
can covalently bond to 4 other C atoms.
What will the shape be?
What will you expect the melting point to be?
Why?
What will you expect the solubility in water to be?
Why?
What will you expect the electrical conductivity to be?
Why?

18. What you need to know:
Diamonds consist of tetrahedrally bonded carbon atoms, i.e. each carbon is covalently bonded to 4 others in a regular arrangement.
You need to be able to draw
one “unit”

19. The many very strong covalent bonds require a lot of energy to break so diamond has a high melting point.
The tetrahedral arrangement of carbons held by strong covalent bonds makes diamond hard.
It does not conduct electricity as there are no free electrons or ions.
It does not dissolve in polar or non-polar solvents as the covalent bonds in the lattice are too strong to be broken by any solvents.

20. Graphite - Another giant covalent crystal
With anomalous properties!

21. Most people first encounter graphite as pencil lead (in fact it's not lead, it's graphite).
In its pure glassy (isotropic) synthetic form carbon fibre, is an extremely strong, heat-resistant (to 3000 °C) material, used in re-entry shields for missile nosecones, solid rocket engines, high temperature reactors and brake shoes.

22. Draw a dot cross diagram to show how 1 C atom
can covalently bond to 3 other C atoms.
What will the shape be?
What will you expect the melting point to be?
Why?
What will you expect the solubility in water to be?
Why?
What will you expect the electrical conductivity to be?
Why?

23. Draw a dot cross diagram to show how 1 C atom
can covalently bond to 3 other C atoms.
What will the shape be?
What will you expect the melting point to be?
Why?
What will you expect the solubility in water to be?
Why?
What will you expect the electrical conductivity to be?
Why?

24. What you need to know:
Each carbon atom is covalently bonded to three other surrounding carbon atoms. These bonds are strong so graphite has a high melting point.
The flat sheets of carbon atoms are bonded into hexagonal structures which exist in layers.

25. Different layers are connected together by weak van der Waals forces
Different layers are connected together by weak van der Waals forces. Therefore, layers of it can slip over each other making it soft.
Graphite can be used as a lubricant as the layers can slip over one another.
Unlike diamond, graphite is an electrical conductor. Delocalised electrons between the layers are free to move in the direction of the current.

26. Iodine - a simple molecular crystal

27. Iodine (from the Greek word Iodes, meaning "violet"), is chemically the least reactive of the halogens.
Iodine is primarily used in medicine, photography and dyes. It is required in trace amounts by most living organisms.
As with all other halogens (members of Group VII in the Periodic Table), iodine forms diatomic molecules, and hence, has the molecular formula of I2.

28. Iodine is a simple molecular substance.
What type of intermolecular forces do you expect there to be in iodine?
Predict (with reasons) the melting point,
electrical conductivity and solubility in water of iodine.

29. What you need to know:
Iodine is a dark grey crystalline solid with a purple vapour.

30. The iodine atoms within each molecule are pulled closely together by the strong covalent bond.
The van der Waals attraction between the molecules is much weaker and are easily broken when heat is applied. This is why the melting point of iodine is low.

31. Iodine does not conduct electricity as there are no free ions or electrons.
Iodine is soluble in non-polar solvents such as hexane because Van der Waals forces form between the molecules and the solvent.

32. electrical conductivity of solid poor good melting and boiling point
The table below shows the structures and some properties of sodium chloride and graphite in the solid state. Explain these properties in terms of bonding and structure. [7]
substance
sodium chloride
graphite
Structure
electrical conductivity of solid
poor
good
melting and boiling point
high
solubility in water
insoluble

33. General
NaCl: ionic/has ionic bonds (1)
Beware of contradictions for this mark, especially reference to intermolecular forces.
Ignore ‘atoms’.
graphite: covalent/giant molecular/macromolecular (1)
Ignore van der Waals’, intermolecular, molecules
Conductivity
NaCl:
ions cannot move/no free ions (or electrons) /mobile ions only in solution or when molten (1)
graphite:
delocalised electrons/ free electrons (between layers)/ electrons conduct (1)
Ignore lone pair

34. melting point
both graphite and NaCl:
bonds are strong/bonds difficult to break /large amount of energy is needed to break bonds (1 for each)
solubility
NaCl:
Water is polar/water has a dipole/ions interacts with water molecules (1)
Graphite:
no interaction with water/
no intermolecular forces with water/graphite is non-polar (1)
QWC: At least 2 complete sentences in which
the meaning is clear. (1)
[8]

35. Jan 2001
6 (a) With the aid of diagrams, describe the structure of, and bonding in, crystals of sodium chloride, graphite and magnesium. In each case, explain how the melting point and the ability to conduct electricity of these substances can be understood by a consideration of the structure and bonding involved. (23 marks)

36. Sodium chloride
Ionic bonding
Giant ionic lattice
Diagram showing alternating +/- ions
High melting point
Strong electrostatic attraction between oppositely charged ions.
Put in a lot of energy to overcome
Doesn’t conduct when solid
No mobile ions/charged particles
Does conduct when molten/solution
Ions free to move

37. Graphite
Covalent bonding.
Macromolecular/giant covalent structure
Diagram
High mp
Strong covalent bonds between atoms
Must put in a lot of energy to break.
Conduct electricity
Free/mobile/delocalised electrons

38. Magnesium
metallic structure and/or bonding
Diagram with labelled +ve ions and delocalised electrons.
High mp
Strong metallic bond
Must put in a lot of energy to break
Conducts electricity
Free/mobile/delocalised electrons