Structure and properties

Question 1

Properties of ionic compounds and why? (4)

Answer 1

1) They have giant structures in which many strong electrostatic forces hold the ions together.
2) High melting and boiling points - high levels of energy needed to overcome electrostatic forces of attraction
3) Can conduct ONLY when molten or in solution - when solid, strong structure means ions are fixed in position and can’t move. In liquid, ions can move around and carry charge and energy
4) Soluble (mostly) - water molecules split up ions in the lattice

Question 2

Properties of simple covalent molecules and why? (3)

Answer 2

1) The atoms within a molecule are held together by strong covalent bonds which act only between the atoms in the molecule, so molecules have little attraction for each other.
2) Low melting and boiling points (often liquid or gas at room temperature) - weak intermolecular forces don’t need much energy to be overcome.
3) Do NOT conduct electricity - molecules have no overall CHARGE

Question 3

Properties of giant covalent structures and why? (2)

Answer 3

1) Very hard - they have rigid structures of strong covalent bonds.
2) High melting and boiling points - It takes a lot of energy to break the strong covalent bonds that form between atoms in the structure and to break down the lattice.

Question 4

What atom is diamond made up of?
Describe the structure of diamond?
Properties of diamond?
What other compound has a similar structure?

Answer 4

Diamond is a form of carbon that has a regular three dimensional shape.
Each carbon atom is covalently bonded to four other carbon atoms, this makes diamond hard and transparent.
Silicon dioxide (silica)

Question 5

Describe the structure, bonding and properties of graphite?

Answer 5

Each carbon atom is covalently bonded to three others, forming giant flat two-dimensional layers, which can slide over one another because there are no covalent bonds between layers. This makes it soft and slippery.

One electron from each carbon atom is delocalised allowing graphite to conduct heat and electricity.

Question 6

What are fullerenes? Describe their structure.

Answer 6

Fullerenes are large molecules formed from hexagonal rings of carbon atoms. The rings join together forming cage-like structures with different numbers of carbon atoms, some of which are nano-sized.

Question 7

Possible usage of fullerenes? (3)

Answer 7

1) Drug delivery to specific parts of a body
2) Catalysts and lubricants
3) Reinforcing materials

Question 8

Properties of metals and why?

What are they useful for making?

Answer 8

Metal atoms are arranged in layers that can slide over one another when a force is applied. They are malleable and ductile, which means they can move into a new position without breaking apart, so the metal bends or stretches into a new shape.
Wires, rods and sheet materials.

Question 9

What are alloys?

Why are alloys harder than pure metals?

Answer 9

Alloys are mixtures of metals or metals mixed with other elements.
Different sized atoms in a metal distort the layers, making it more difficult for them to slide over each other, making alloys harder than pure metals.

Question 10

What are shape memory alloys?

Answer 10

Alloys that can be bent or deformed into a different shape, but return to their original shape when they are heated e.g. dental braces.

Question 11

On what do the properties of a polymer depend? (2)

Answer 11

1) The monomers used to make it

2) The conditions to carry out the polymerisation reaction

Question 12

Describe the structure and bonding of thermosetting polymers and their properties. (2)

Describe the structure and bonding of thermosoftening polymers and their properties. (3)

Answer 12

Thermosetting
1) These do not melt or soften when we heat them.
2) These polymers set hard when they are first moulded because strong covalent bonds form cross links between their polymer chains.
3) The strong bonds hold the polymer chains in position.
Thermosoftening
1) They are made up of individual polymer chains that are tangled.
2) They soften with heat, and harden again when cooled.
3) This means they can be heated to mould it into shape and it can be remoulded by heating it again.

Question 13

1 nanometre is how many metres?

Answer 13

1x10^-9 (0.000000001m or a billionth of a metre)

Question 14

Define nanoscience.

Answer 14

The study of small particles that are between 1 and 100 nanometres in size.

Question 15

What about them makes nanoparticles useful?

Answer 15

They have a high surface area to volume ratio so they are extremely reactive and have other properties that can make them very useful.

Question 16

What makes low density (LD) poly(ethene) different from high density (HD) poly(ethene)?
What is the difference between the two?

Answer 16

They are produced using different catalysts and reaction conditions.
HD poly(ethene) is harder and has a higher softening temperature than LD poly(ethene).

Question 17

How does nanotechnology use nanoparticles? (5)

Answer 17

As:

1) Highly selective sensors.
2) Very efficient catalysts.
3) New coatings.
4) New cosmetics such as sunscreens and deodorants.
5) And to give construction materials special properties.

Question 18

What is a drawback of the use of nanoparticles?

What must be done about this?

Answer 18

As they are used more and more there will be a greater risk of them finding their way into the air and into our bodies. This could have unpredictable consequences on our health and the environment.
More research must be done to find out their effects.