When can ionic substances conduct electricity?
When molten or dissolved in water.
Why can ionic substances conduct electricity when molten or when dissolved in water?
The ions can move freely.
This allows them to carry electrical charge➡️the liquids conduct electricity.
What are the properties of simple molecules?
-Low boiling points.
-Low melting points.
-Do not conduct electricity.
Why do simple molecules have low boiling and melting points?
The intermolecular forces between simple molecules are weak, so little energy is needed to overcome them.
Why don't simple molecules conduct electricity?
Simple molecules have no overall charge, so they cannot carry electrical charge and do not conduct electricity.
Why do substances with giant covalent structures have very high melting points?
Every atoms in a giant covalent structure is joined to several other atoms by strong covalent bonds➡️Takes a lot of energy to break the lattice➡️High melting point.
What are diamond and graphite made of?
What is the structural difference between diamond and graphite?
Each carbon atom in diamond is covalently bonded to four others, whilst every carbon atom in graphite is covalently bonded to three others.
What differences in properties are there between diamond and graphite and why?
Diamond= Hard and transparent➡️Strong bonds Graphite= Slippery and Grey➡️No covalent bonds between each layer so they slide over each other
What are fullerenes?
Fullerenes are large molecules formed from hexagonal rings of carbon atoms.
Why can graphite conduct electricity and not diamond?
Graphite can conduct electricity (and heat) because of the delocalised electrons in its structure.
Diamond doesn't have any delocalised electrons, so is a poor conductor.
Why can metals be made into wires?
Metal atoms are arranged into layers which can slide over each other, so we can bend or stretch it into a new shape without it breaking.
What are alloys?
Alloys are mixture of metals mixed with other elements.
Why can alloys be more useful than pure metals and why?
Alloys are harder than pure metals because the different sized atoms distort the layers, making it more difficult for them to slide over each other.
What do shape memory alloys do?
Shape memory alloys can be bent or deformed into a different shape, but can be returned to their original shape when heated.
Why are metals good conductors of electricity?
Metal structure have delocalised electrons, which move through the giant metal lattice and can transfer energy quickly which makes them good conductors of heat and electricity.
Why do low density poly(ethene) and high density poly(ethene) have different properties?
They are made using different catalysts and different reaction conditions.
As a result, HD poly(ethene) has a higher softening temperature and is stronger than LD poly(ethene).
Describe the structure of thermosetting polymers and their properties.
Thermosetting polymers set hard when they are first moulded because strong covalent bonds form cross-links between their polymer chains. Thermosetting polymers do not soften or melt when heated.
Give an example of a thermosoftening polymer, and describe its structure and bonding and explain why thermosoftening polymers melt when heated.
Made up of individual polymer chains that are tangled together (like spaghetti). Weak intermolecular forces, so bonds are easily overcome with little energy. Thermosoftening polymers soften or melt easily when heated.
What allows thermosoftening polymers to be remoulded?
In thermosoftening polymers the forces between the chains are weak.
When we heat the polymer, the weak intermolecular forces are broken and the polymer becomes soft. When the polymer cools down, the intermolecular forces bring the polymer back together so the polymer hardens again.
Nanoscience is the study of small particles between 1 and 100 nanometers in size.
What is special about nanoparticles?
1 million nanoparticles= 1mm.
Their very small sizes give them a very large surface area, so nanoparticles behave differently from the bulk materials they are made from, resulting in new properties.
Give some examples of nanoscience.
-Make Up and Moisturiser.
What are some of the properties of nano-silver?
Nano-silver has antibacterial, antiviral and anti fungal properties.
These tiny pieces of silver are incorporated into materials to make clothes and medical dressings which stay fresh for longer.
What are the advantages and disadvantages to nanoscience?
A-Unusual properties leading to new uses.
A- Could be used to make very efficient catalysts.
A-Some have antibacterial, anti fungal and antiviral properties.
D-Increased use increases risk of them getting in the air and into our bodies➡️Unpredictable consequences on health and environment.
Why do ionic solids have high melting points?
Ionic compounds are all solid at room temperature, and a lot of energy is needed to overcome the ionic bonds to melt the solids because of the strong electrostatic forces holding the ions together.
Explain why, in terms of structure, carbon dioxide is a gas, even at low temperature.
Has simple molecules (1). Weak intermolecular forces (1) so little energy is needed to overcome (1).
Name the ion which makes sulfuric acid solution acidic.
Nitinol is an alloy used in dental braces- suggest why this is.
Nitinol is a smart alloy, so can remember it's original shape.
Carbon atoms are bonded in a nanotube like a single layer of graphite.
Suggest why carbon nanotubes are used as lubricants (2 marks).
Nanotubes slide over each other (1) because there are no covalent bonds between the nanotubes (1).