C2.3 Properties Of Materials

Different forms of an element in the same state but with different atomic arrangements Example: Diamond and graphite are 2 different allotropes of carbon

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

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

Change directly from a solid to a gas

Change directly from a gas to a solid

Substance that cracks or breaks when a external force is applied Eg. Concrete

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

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

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

Between 1nm and 100nm across Consists of just a few 100 atoms LARGER than atoms

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

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

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

Metal - metallic bonds - strong Example: iron, mercury

Ionic compound - ionic bonds - strong - sodium chloride

Covalent bonds - strong - diamond Silicon dioxide is ALSO a giant covalent structure

Simple molecule - intermolecular forces - weak - oxygen

Acrylic strip

Chemical changes when chemical reactions occur Involve formation of new chemical elements or compounds Physical change: a substance simply changes physical state. For example, from a solid to a liquid

Ceramic

Silver Tin Copper

Copper Zinc

Tin Lead