C2.3 Properties Of Materials Flashcards
What is an allotrope
Different forms of an element in the same state but with different atomic arrangements
Example: Diamond and graphite are 2 different allotropes of carbon
What happens when a substance changes state
When it melts or boils, forces of attraction between its particles are overcome
Some break going from solid to liquid
All remaining break when going from liquid to a gas
Bonds form when a substance condenses or freezes
Some form going from gas to a liquid
Many form going from liquid to solid
Stored chemical energy is transferred to the surroundings, usually by heating when chemical bonds form
Types of bonding
Metals | ionic compounds (sodium chloride) | giant covalent structures (graphite) - usually in the solid state at room temperature
Simple molecular substances (wax candle) are in the liquid state at room temperature, or as a solid but easily melted
Sublimation
Change directly from a solid to a gas
Deposition
Change directly from a gas to a solid
Brittle substances
Substance that cracks or breaks when a external force is applied
Eg. Concrete
Why are metals strong and malleable
Metal ions are held in a LATTICE by forces that attract them to a “sea” of delocalised electrons
When a large external force is applied the layers of metal ions slide over one another
Delocalised electrons are free to move, overall no bonds are broken
Why are giant covalent structures brittle
Contain very many atoms held together in a giant lattice by strong covalent bonds
If large force applied, many covalent bonds break at once and the substance breaks
Same applies to ionic compounds
Why some substances conduct electricity
They have charged particles that are free to move
Metals do this as they have delocalised electrons free to move through the lattice
Ionic compounds do this when molten or dissolved but not as a solid
Graphene - forms 3 covalent bonds with other carbon atoms and fourth electron delocalised
How big are nanoparticles
Between 1nm and 100nm across
Consists of just a few 100 atoms
LARGER than atoms
What gives nanoparticles their useful properties
A substance made from nanoparticles is called a nanoparticulate
Nanoparticles have different properties to the same substance in bulk
Nanoparticles are used to make paints and cosmetics
Properties due to their very large surface area to volume ratio, compared to that of the substance in bulk
These properties have helped develop
New catalysts
Self cleaning windows, ovens an clothes
Surface area to volume ratio
Ratio = surface area / volume
Surface area to volume ratio can also affect the properties of substances in bulk
For example powders dissolve and react faster than lumps of the same material
Biological example:
Surface area to volume ratio decreases as organism gets larger
This has important implications for the efficiency of exchange surfaces, as larger organisms require a larger surface area to sustain the necessary exchange of materials
Risks of nanoparticles
Could be breathed in
Could be absorbed by the skin or pass into cells
Take a long time to break down once released into the environment
Toxic substances could stick to their surfaces
Metallic bonding
Metal - metallic bonds - strong
Example: iron, mercury
Ionic compounds
Ionic compound - ionic bonds - strong - sodium chloride
