Materials and their Properties
Material is what something is made up of. There are five typical materials:
- Metals - strong, shiny, good conductors of heat and electricity. Some are magnetic.
- Plastics - good insulators of electricity and can be coloured. Some melt easily, some are acid resistant, some are flexible, easily shaped and light weight
- Glass - often transparent or translucent. Hard by very brittle and can be coloured
- Fibres - natural or synthetic. Made of tiny threads and so can be strong and usually quite bendy
- Ceramics - can withstand high temperatures. Hard, brittle and very strong if compressed
Property of a material is how it behaves. A material is choosen because of its properties. Some properties of materials are:
- Strong - does not change shape and does not break easily
- Hard - cannot be scratched or dented easily
- Brittle - hard but will break easily
- Malleable - shaped easily with a hammer
- Magnetic - attracts to magnets
- Transparent - see-through
- Translucent - lets light through but can't see through it clearly
- Flexible - bent easily without breaking
- Conductor of Electricity - lets electric current pass through it
- Conductot of Heat - lets heat pass through it easily
- Insulator of Electricity - does not let an electric current pass through it
- Insulator of Heat - does not let heat pass through it easily
Properties of Metals
Metals are typically:
- solid at room temperature (except mercury)
- shiny when polished or freshly cut (reflects light) but can be tarnished from reaction with oxygen/air
- high density (heavy)
- high melting and boiling points (Cu 1085/2562°C, Fe 1538/2862°C, tungsten (W) 3422/5555°C)
- conduct heat (free electrons to transfer heat energy)
- conduct electricity (flow of electrons)
- strong but also bendy and malleable (beaten into a thin sheet)
- ductile (drawn into a wire)
- can be mixed together to form alloys (steel is iron with 1% carbon and much less brittle tahn iron; bronze is copper and tin - harder than copper but still easily shaped; coins are make of cupro-nickel with copper and nickel (75%:25%))
The common metals that are ferromagnetic (forms permanent magnet) at room temperature are iron, nickel and cobalt. Chromium shows anti-ferromagnetic ordering at room temperature (and below) but above 38°C, it transforms into a paramagnetic state.
The properties are due to the metallic crystal structure of metals which is a gaint structure of atoms held together by metallic bonds, allowing the outer electron(s) of each atom to move freely
Properties of Non-Metals
Non-metals are typically:
- solid or gas at room temperature (about half are solids and other half are gases. Bromine is the only liquid non-metal element)
- as solids dull and brittle
- low density (light)
- poor conductors of heat
- do not conduct electricity (except graphite which has a crystal structure of carbon 'layers' with some free electrons)
- easily broken (brittle)
- never magnetic
Non-metals usually bond in small molecules (e.g. O2, N2 etc). However, silicon and carbon form gaint structures and carbon can exists as graphite or diamond.
Metal or Non-Metal
Using physical properties to decide whether an element is a metal or non-metal can be unreliable. Iodine (a non-metal) is shiny like a metal and carbon in the form of graphite is a good conductor of electricity. The best way of deciding is to use chemical properties.
If an element is burned in oxygen an oxide is produced. If the oxide is tested with Universal indicator and found to be acidic (pH value less than 7), the oxide produced is a non-metal. The element is a metal if the oxide has a pH of 7 (neutral) or greater (alkaline).