1.5 Solid Structures

Question 1

Describe the crystal structure of sodium chloride

Answer 1

Question 2

Describe the crystal structure of caesium chloride

Answer 2

Question 3

Name two giant covalent structures formed from carbon atoms

Answer 3

• Graphite
• Diamond

Question 4

Describe the structure of graphite

Answer 4

• Each carbon atom is bonded to 3 other carbon atoms.
• Layers of hexagonal rings of carbon atoms form.
• There are weak intermolecular forces between layers.
• There is one delocalised electron per carbon atom.

Question 5

Describe and explain the properties of graphite

Answer 5

• Graphite is soft/slippery because there are only weak intermolecular forces between layers which allow the layers to slide over one another.
• Graphite conducts electricity because there is one delocalised electron per carbon atom. The delocalised electrons can carry charge.

Question 6

Describe the structure of diamond

Answer 6

• All carbon atom are covalently bonded to four other carbon atoms.
• There are no delocalised electrons.

Question 7

Describe the properties of diamond

Answer 7

• Very hard.
• Very high melting point.
• Doesn’t conduct electricity as there are
  no charged particles.

Question 8

What are the uses of graphite? Why?

Answer 8

Electrodes: Graphite conducts electricity and has a high melting point.

Lubricant: Graphite is slippery (the layers in graphite can slide over each other).

Question 9

Why is diamond used in cutting tools?

Answer 9

Diamond is very hard.

Question 10

Describe the structure of ice

Answer 10

Ice has a lower density but takes up a greater volume when compared to water. This is due to the presence of hydrogen bonding between water molecules. These strong intermolecular forces stay rigid when ice forms and position the water molecules further apart than in liquid water. Therefore, a sample of ice will occupy a greater volume than the water it formed from.

Question 11

What type of structure is iodine?

Answer 11

Iodine is a simple molecular compound. There are covalent bonds between the iodine atoms and weak temporary dipole interactions between the molecules.

Question 12

Describe metallic bonding

Answer 12

Metallic bonding occurs in metals. The positive metal ions are held together in a sea of delocalised electrons.

Question 13

Explain the electrical conductivity of ionic compounds

Answer 13

Ionic compounds cannot conduct electricity when solid. They are able to conduct electricity when molten or aqueous because in these states the ions are free to move and carry charge.

Question 14

Explain the electrical conductivity of a covalent compound

Answer 14

Generally, covalent compounds do not conduct electricity because there are no free charged particles.

Question 15

Explain the electrical conductivity of a metal

Answer 15

Metals are able to conduct electricity because the delocalised electrons are free to move and carry charge.

Question 16

Compare the melting points of simple covalent molecules and macromolecules

Answer 16

Macromolecules have higher melting points than simple molecules. To melt the simple molecules the intermolecular forces need to be overcome, whereas to melt the macromolecules the covalent bonds have to be broken. A lot less energy is required to overcome the intermolecular forces compared to breaking lots of covalent bonds, so simple molecules have lower melting points.

Question 17

Explain how the hardness of metals can be improved

Answer 17

Metals are made up of atoms in uniform rows which can slide over each other very easily. This makes a metal very malleable.
Metals can be turned into alloys in order to increase the hardness. This involves combining different metals so that the different sized atoms distort the neat layers, making it harder for the layers to slide over one another.