AQA Chemistry - Unit 2 - Structure and properties

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Why do ionic compounds have high melting and boiling points?
Ionic compounds have giant structures held by strong electrostatic forces. Each ion in the compound is surrounded by an oppositely charged ion. A lot of energy is needed to overcome the ionic bonds and so they have high melting/boiling points.
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What state are giant ionic structures at room temperature?
Solid
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Why can ionic compounds conduct electricity when molten or in liquid form?
When ionic compounds are melted the ions are free to move around. This allows their electrons to carry and electrical charge.
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Do ionic compounds conduct electricity in solution?
Some ionic solids conduct electricity in water because they are soluble in water; the water molecules break the ionic lattice so electrons are free to move.
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Why do simple molecules like Oxygen not conduct electricity?
They have no overall charge so cannot carry electrical charge.
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Why do simple covalent structures have low melting and boiling points?
The intermolecular forces between simple molecules are weak and so little energy is needed to overcome them. This means simple molecules are usually gas or liquid at room temperature.
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Why do giant covalent structures (macromolecules) like diamond have very high melting points?
Each atom in the structure in covalently bonded to several over atoms so so an enormous amount of energy is needed to break the bonds.
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Explain the structure of diamond.
Diamond is a form of carbon that has a regular three-dimensional giant structure. Each carbon atom is covalently bonded to four other carbon atoms. This makes diamond hard and transparent.
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Which compound shares a similar structure to that of diamond?
Silicon dioxide (silica)
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Explain the structure on graphite.
Graphite is 2-D. It is a form of carbon where each carbon bonds to three to three other carbon atoms forming a flat sheet of hexagons.
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Why is graphite slippery and grey, why can it conduct electricity ?
There are no covalent bonds between the layers so the inter-molecular forces are weak .The layers can therefore slide voer eachother and so graphite is slippery with grey colour. An electron in each carbon atom is delocalised - conduct electricity.
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Describe fullerenes.
Fullerenes are large molecules form from hexagonal rings of carbon.The rings join to form cages.
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Name some uses of fullerenes.
Drug delivery into the body. Lubricant. Catalysts. Reinforcing materials.
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Why are metals malleable (bendy) ?
Metals can be bent into, for example, wires, because their atoms are all the same size. When we apply a force the atoms arranged in layers slide over each other and we can bend it!
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Why are alloys harder than pure metals?
Alloys have a mixture of metal atoms of different sizes and so their layers cannot slide over eachother.
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How can shape memory alloys be used?
In dental braces; even after being bent or melted shape memory alloys return to their original shape.
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Why are alloys more useful than pure metals?
They are harder and stronger and be designed for specific uses.
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Why do LD and HD poly(ethene) have different properties?
They were formed under different reaction conditions and catalysts.
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What is the difference between HD polyethene and LD polyethene?
HD polyethene has a higher softening temperature and is stronger than LD polyethene.
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What are the differences between thermosoftening and thermosetting polymers?
Thermosoftening polymers melt and soften and are made of tangled individual polymer chains. Thermosetting polymers not not melt or soften - they have cross links which are strong covalent bonds to hold polymer chains in position.
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Why can thermosoftening polymers be remoulded?
There are weak intermolecular forced between the polymer chains and so they can be broken easily. When the polymer cools down again the forces bring the chains back together again.
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What is a nanoparticle?
A very small particle made from hundred of atoms a few nanometres in size.
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How big is a nanometre?
One billionth of a metre (10^-9m)
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Why do nanoparticles behave differently than larger particles?
They have a large surface area to volume area and so they can react more.
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What uses do nanoparticles have?
Catalysts, cosmetics such as deodorant and sun cream, to give construction materials special properties.
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Scientists have developed a new deodorant using nanoparticles. What should be done before it is sold to the public?
Effects on the body and the environment should be researched because the nano-particles could react in a different way than normal particles and be potentially dangerous.
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Other cards in this set

Card 2

Front

What state are giant ionic structures at room temperature?

Back

Solid

Card 3

Front

Why can ionic compounds conduct electricity when molten or in liquid form?

Back

Preview of the front of card 3

Card 4

Front

Do ionic compounds conduct electricity in solution?

Back

Preview of the front of card 4

Card 5

Front

Why do simple molecules like Oxygen not conduct electricity?

Back

Preview of the front of card 5
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