Topic 2 Flashcards
Ionic compounds
Regular lattice structure. Structure is called giant ionic lattice. Very strong electrostatic forces of attraction between oppositely charged ions, in all directions of the lattice. High melting & boiling points due to the strong bonds between the ions. When solid, cannot conduct electricity due to the lack of delocalised electrons. When molten or aqueous, ions are free to move so will carry electric charge. Lots of energy required to overcome the electrostatic forces of attraction.
Giant covalent structures
Macromolecules. Bonded by strong covalent bonds. Very high melting and boiling points as lots of energy is required to break the covalent bonds between the atoms. No charged particles so they don’t conduct electricity.
Diamond
Giant covalent structure. Each carbon atom forms four covalent bonds in a very rigid, giant covalent structure. Only made up of carbon atoms. Bonds makes diamond really hard. Very high melting point. Doesn’t conduct electricity
Graphite
Each carbon atom forms three covalent bonds to create layers of hexagons. Each carbon atom has one delocalised electron. Layers of hexagons are held together weakly (no covalent bonds between layers) so they are free to move over each other which makes graphite soft and slippery. Ideal as a lubricating material. Very high melting point. One delocalised electron conducts electricity and thermal energy
Graphene
One layer of graphite. The sheet is just one atom thick, making it a two-dimensional substance. Very strong but very light. Can be added to composite materials to improve their strength without adding much weight. Contains delocalised electrons so can conduct electricity so it can be used in electronics.
Fullerenes
Form spheres and tubes. Molecules of carbon shaped like closed tubes or hollow balls. Mainly made up of carbon atoms arranged in hexagons but can also contain pentagons or heptagons. Fullerenes can be used to ‘cage’ other molecules as the fullerene structure forms around another atom or molecule which is then trapped inside. This can be used in medicine to deliver a drug to the body. Huge surface area so they could make great industrial catalysts. They can also make great lubricants. Can form nanotubes (tiny carbon cylinders) - Length:diameter is very high. Nanotubes conduct electricity and thermal energy. High tensile strength. Nanotubes can be used in electronics or to strengthen materials without adding much weight such as tennis racket frames.
Alloys
Harder than pure metals. Mixture of two or more metals or a metal and another element. Due to the different sized atoms, the layers of atoms are distorted and it is more difficult for them to slide over each other which makes alloys harder than pure metals
Nano particles
Diameter between 1nm - 100nm. Nano science investigates the use of nano particles. Large surface area to volume ratio so they could help make new catalysts. Absorbed more easily by the body so they could deliver drugs to specific cells. Can be used in tiny electric circuits for computer chips. Silver nano particles have antibacterial properties so they can be added to polymer fibres that are then used to make surgical masks and wound dressings - also can be added to deodorant. Nano particles can also be used in cosmetics e.g. improve moisturisers without making them oily. We don’t know the long term effect on health (whether they might damage cells) or its damage to the environment.
Ceramics
Non metal solids with high melting points that aren’t made from carbon based compounds. E.g. clay - can be moulded when wet but hardens to form a clay ceramic when fired at high temps. Ideal for pottery and bricks. Glass is also a ceramic - moulded when hot, brittle when thin and cooled.
Composites
One material embedded in another. Fibres or fragments of a material (known as the reinforcement) are surrounded by a matrix acting as a binder. Properties of a composite depend on the properties of the materials it is made from. Fibreglass consists of fibres of glass embedded in a matrix made of polymer (plastic). Fibreglass has a low density but is very strong and is used for skis, boats and surfboards. Carbon fibre composites also have a polymer matrix and the reinforcement is from carbon nanotubes or carbon fibres. Very strong and light so are used in aerospace and sports car manufacturing.
Concrete is made from aggregate embedded in cement. Very strong and used as a building material e.g. skate parks.
Wood is a natural composite of cellulose fibres held together by an organic polymer matrix.
Polymers
Can have very different properties. Properties depend on how it’s made and what it’s made from. E.g. poly(ethene) properties depend on the catalyst that was used and the reaction conditions (temperature and pressure). Thermosoftening polymers can be melted and remoulded. Thermosetting polymers are strong, hard and rigid and don’t soften when heated due to the cross links between the polymer chains, forming a solid structure.
