C2.2 Structure and Properties
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Explain why NaCl is a solid at room temperature
It has a giant ionic lattice It is held together by ionic bonds which are very strong Therefore it has a high melting point
Explain why oxygen is a gas at room temperature
It has a simple molecular structure It is held together by weak intermolecular forces Therefore it has a low melting point
Explain why iron is a solid at room temperature
It has a giant metallic structure It is held together by strong metallic bonds Therefore it has a high melting point
Explain why iron conducts electricity as a solid and liquid
It has delocalised electrons which are free to move throughout the metal structure
Explain why graphite conducts electricity
Each carbon has only 3 bonds. This leaves one delocalised electron Which is free to move
Explain why diamond doesn’t conduct electricity
Each carbon has 4 bonds. It has no free electrons
Explain why sodium chloride doesn’t conduct electricity as a solid
The ions can’t move
Explain why sodium chloride conducts electricity when dissolved
The ions are free to move
Explain why carbon dioxide doesn’t conduct electricity
Its electrons aren’t free to move
Explain why molten magnesium chloride can conduct electricity
The ions are free to move
Explain why ammonia is a gas at room temperature
It is a simple molecular substance Its held together by weak intermolecular forces Therefore it has a low melting point
Explain why methane is a gas at room temperature
It is a simple molecular substance It is held together by weak intermolecular forces Therefore it has a low melting point
Explain why silicon dioxide has an unusually high melting point
It has a giant covalent structure It has strong covalent bonds Which require a lot of energy to break
Explain why graphite has a very high melting point
It has a giant covalent structure which is held together by strong covalent bonds which require a lot of energy to break
What property makes diamond useful for sharpening knives
It is very hard
Explain why diamond is so hard
It is arranged in a giant lattice Each carbon has 4 bonds The lattice is rigid
Explain why thermosetting polymers have high melting points
They have crosslinks between the chains made with covalent bonds which are strong
Explain why high density polyethene has a higher melting point than low density polyethene
High density polyethene has a crystalline structure and strong forces between the polymer chains
What is a nanoparticle
a particle between 1nm and 100nm in size
Why do nanoparticles have different properties?
Because they have a much bigger surface area
What are the risks of nanoparticles?
Their large surface area makes them very reactive/explosive (nano aluminium) Nanoparticles are easily absorbed by the lungs and there is little research into the long term health risks.
What conditions can be changed to make High Density Polyethene rather than Low Density Poly Ethene?
Pressure Temperature