giant covalent structures, metallic bonding and modern materials

structure of graphite

a giant covalent structure with…

- 2D layers of hexagonal rings with strong bonds

- delocalised electron between layers makes it conductive/helps layer bond

- weak bonds between layers

structure of diamond

• 3D lattice structure

• each carbon atom forms 4 very strong covalent bonds

silicon dioxide structure

• 3D lattice structure

• 2 oxygen atoms for each silicon atom

properties of graphite

• insoluble in water

• conducts electricity

• soft/slippery between layers

• high melting point

properties of diamond

• insoluble in water

• can’t conduct electricity

• high melting point

• strong and lustrous

giant covalent structure

a huge network of atoms held by strong covalent bonds

metallic bonding

electrostatic attraction between positive metal ions in a regular lattice structure and a ‘sea’ of delocalised electrons (from the outer shell)

why can metals conduct electricity and heat?

the delocalised electrons are free to move and carry charge through the structure

why do metals have strong melting points

a lot of energy is needed to break strong bonds between ions/electrons

malleable/ductile

can be bent into different shapes/can be stretched (without breaking)

why are alloys harder than pure metal

• pure metal is soft due to the regular arrangement, which means layers can slide over each other

• alloys are harder because different size atoms disrupt arrangement/can’t slide over each other

nanoscience

study of nanoparticles 1-100 nm in size

material behave differently at the nanoscale because…

• large surface area to volume ratio

• means high percentage of atoms exposed at surface

• therefore very reactive/effective as catalysts

structure/properties of graphENE

a single layer of graphite made of hexagonal rings of carbon atoms

very conductive and flexible→portable electronics

structure/properties of spherical fullerenes e.g. Buckminsterfullerene (bucky balls)

hollow 3D sphere made of hexagonal rings of carbon atoms

slippery→ lubricants

structure/properties of cylindrical fullerenes e.g. nanotubes

3D hollow tube of graphene made of hexagonal rings of carbon atoms

strong, light, conductive→ catalysts

polymer

a long chain molecule made of many small molecules called monomers joined together

addition polymerisation (e.g. ethene)

chemical reaction where double bonds in the monomers break to create a single bond and 2 free electrons that can join to others

properties of plastics

soft/hard, flexible/brittle etc

• depend on what monomer they are made from and conditions under which polymer was made

thermosettting vs thermosoftening plastics

• thermosetting has high melting points due to cross-links between chains

• thermosoftening has lower melting point due to no cross-links