C2.2 Structure, Properties and Uses of Substances Flashcards
Ionic compounds have a regular arrangement of ions called…
A giant ionic lattice
Why do ionic compounds have high melting and boiling points?
Because they have strong electrostatic attractions between ions - which require a large amount of energy to be overcome
What happens when ionic compounds melt?
There are ions are free to move, and will carry electric charge
What happens when ionic compounds dissolve in water?
Ionic compounds dissolve easily in water, the ions separate and are free to move so they carry electric charge
What are simple molecules?
Substances with covalent bonds, and molecules made up of only a few atoms e.g. Hydrogen and Oxygen (which travel in pairs)
What are the properties of simple molecules?
They have low melting and boiling points, they are mostly gas or liquid at room temp, and they don’t conduct electricity
Why do simple molecules have low melting and boiling points?
The intermolecular forces between the molecules are extremely weak and can be easily overcome.
What are the differences between giant covalent structures and giant ionic structures (lattices)?
They are similar, but giant covalent structures have no charged ions, all atoms are bonded to each other by strong covalent bonds and they do not conduct electricity
Do giant covalent structures have high or low melting/boiling points?
High, because they have strong covalent bonds between energy which require a lot of energy to be overcome
What are examples of giant covalent structures?
Diamond, graphite and silicon dioxide
What is the structure of a diamond?
Each carbon atom forms 4 covalent bonds in a very rigid giant covalent structure - diamond is the hardest natural substance and is used for drill tips
How is graphite structured?
Each carbon atom only form 3 out of a possible 4 covalent bonds, this creates layers of carbon atoms
What does the layers in graphite mean it can do?
The layers are free to slide over each other because there are no covalent bonds between them - the layers can be rubbed off on paper (pencil). Graphite is soft and slippery
How are the layers in graphite held together?
Weak intermolecular forces hold the layers together, but these forces are easily overcome
Is graphite a good conductor?
Because the carbon atoms have only formed 3 out of 4 possible covalent bonds, there are delocalised electrons which can move freely throughout the layers - making graphite a good conductor of heat and electricity
How are metals structured?
Metal atoms are held together in a regular structure
Why can metals be bent and shaped?
The atoms form layers that are able to slide over each
Why are metals good conductors of heat and electricity?
Because they have delocalised electrons that are free to move through the whole structure - these electrons carry the current and heat energy through the structure
What are alloys?
Two or more metals mixed together
Why are alloy harder than pure metals?
Because they contain different sized atoms (as elements have different sized atoms) which makes it harder for the atoms to slide over each other
What are nanoparticles?
Tiny particles 1-100 nanometres across
What properties do something silver nanoparticles have compared to the bulk chemical?
Silver nanoparticles kill bacteria and are used in surgical masks, normal silver particles are much bigger and can’t kill particles
What new uses of nanoparticles are being developed?
Nanoparticles have a huge surface area so they could be used as catalysts, nanotubes can be used to make stronger, lighter building materials, new cosmetics like sun tan cream and deodorant - they do their job and don’t leave white marks on the skin, lubricant and nanotubes could be used in electrical circuits for computer chips
What are fullerenes?
A type of nanoparticle
How are fullerenes structured?
Molecules of carbon arranged in hexagonal rings, are shaped like hollow balls or closed tubes
What are uses of fullerenes?
Lubricants, catalysts, medicine - they’re easily absorbed by the skin so could help deliver drugs to a specific location and fullerenes can be joined to make nanotubes
Properties of nanotubes?
The covalent bonds make carbon nanotubes very strong, they can be used to reinforce materials like graphite in tennis rackets
What is a polymer?
Very large molecules formed of many small molecules (monomers)
How are polymers bonded?
Strong covalent bonds hold the atoms together in long chains
Name two different types of polymers
Thermosoftening and thermosetting polymers
What are thermosoftening polymers made of?
Individual tangled chains of polymers like spaghetti
How are thermosetting polymers structured?
They have cross-links between polymer chains
What are the properties of thermosetting polymers?
Due to the cross-links, they don’t melt when heated, when it reaches a certain temperature it just burns
What determines the properties of a polymer?
The intermolecular forces between the polymer chains
Why are thermosetting polymers strong, hard and rigid?
The cross-links between the polymer chains are very strong - holding the chains firmly together in a solid structure
How are the chains held together in thermosoftening polymers?
They have weak intermolecular forces between chains, and are free to slide over each other. These forces are very weak and are easy to overcome so the plastic is easy to melt.
What happens when thermosoftening polymers cool after melting?
The polymer hardens into a new shape, you can melt these polymers and remould them as many times as you like making it easy to recycle
How are different types of polythene made?
By using different conditions when being made
How is low density polythene made?
By heating ethane to about 200°C under high pressure
What are the properties of low density polythene?
It is flexible and used for bags and bottles
How is high density polythene made?
Made at low temperatures, low pressure and is with a catalyst
Properties of high density polythene
Rigid and used for water tanks and drainpipes
What are smart materials?
Substances that behave differently depending on the condition
What are shape memory alloys?
A type of smart material - it’s shape can be changed, but they will return to their original shape when heated
