C2.2 How structure influences the properties and uses of substances Flashcards
What are substances that consist of simple molecules?
Gases, liquids or solids that have relatively low melting and boiling points
What forces do substances that consist of simple molecules have between the molecules?
Weak intermolecular forces
Which forces are overcome in a simple molecular substance?
The intermolecular forces, not the covalent bonds
Why do substances that consist of simple molecules not conduct electricity?
They do not have an overall electric charge
What are some examples of substances that consist of simple molecules?
Chlorine, oxygen and water
What structures do Ionic compounds have?
Regular structures, Giant Ionic Lattices
What do Giant ionic lattices have?
Strong electrostatic forces in all directions between oppositely charged ions
Why do ionic compounds have high melting and boiling points?
Because large amounts of energy are needed to break the many strong bonds
When do ionic compounds conduct electricity and why?
When melted or dissolved in water because the ions are free to move and carry the current
What can atoms that share electrons also form aside form simple molecular substances?
Giant covalent structures / macromolecules
What are some example of giant covalent structures (lattices)?
Diamond, silicon dioxide and graphite
How are atoms linked in giant covalent structures?
By strong covalent bonds
What do the strong covalent bonds in giant covalent structures result in them having?
Very high melting and boiling points
In diamond, how many covalent bonds does each carbon atom form?
Four, so diamond is very hard
In graphite, how many covalent bonds does each carbon atom form?
Three, forming layers
Why is graphite soft and slippery?
There are no covalent bonds between the layers so they are free to slide over each other
Why can the layers of graphite be rubbed off so easily?
There are weak intermolecular forces between the layers
Why is graphite a good conductor of heat and electricity?
Because each carbon atom has a delocalised electron which can move freely through the structure carrying the current, allowing graphite to conduct heat and electricity
What else can carbon atoms form?
Fullerenes with different numbers of carbon atoms
What is the structure of fullerenes?
Hexagonal rings of carbon atoms
What can fullerenes be used for?
Drug delivery into the body, in lubricants, as catalysts, and in nanotubes for reinforcing materials e.g. in tennis rackets
Why do metals conduct heat and electricity?
Because of their delocalised electrons which are free to move around the whole structure
Why can metals be bent and shaped?
The layers in metals are free to slide over each other
What are alloys?
They are made up of two or more different metals
Why are alloys harder than pure metals?
The different sized atoms of the metals distort the layers in the structure making it more difficult for them to slide over each other
What can shape memory alloys do?
Return to their original shape after being deformed
What is an example of a shape memory alloy?
Nitinol used in dental braces
How does nitinol work in dental braces?
Nitinol can change shape when cooled but when heated it returns back to its original shape. When used for dental braces it warms in the mouth then tries to return to its remembered shape and pulls the teeth with it
What do the properties of polymers depend on?
What they are made from and under what conditions
How are low density and high density poly(ethene) produced?
Using different catalysts and different reaction conditions
What are the properties of low density poly(ethene)?
It is flexible
How is low density poly(ethene) made?
By heating ethene to about 200 degrees under high pressure
What are the properties of high density poly(ethene)?
It is rigid
How is high density poly(ethene) made?
At lower temperatures and lower pressure with a catalyst
What do thermosoftening polymers consist of?
Individual, tangles polymer chains
What do thermosetting polymers consist of?
Polymer chains with cross links between them so that they do not melt when they are heated
What holds thermosoftening polymers together?
Weak intermolecular forces so they are free to slide over each other. This makes them easy to melt and remould these plastics
What holds thermosetting polymers together?
Strong intermolecular forces between the chains making them strong, hard and rigid
What size are nanoparticles?
1-100 nanometres
How many atoms do nanoparticles roughly contain?
100 atoms
Why could nanoparticles help as catalysts?
They have a huge surface area compared to volume
What can nanoparticles be used to make?
New stronger and lighter construction materials, new cosmetics such as sun tan lotions and deodorants, new catalysts, new medicine, new lubricant coatings, new computers, highly selective sensors
What can fullerenes be joined together to form?
Nanotubes
