Atoms and Elements
Atoms have a nucleus which contains protons and neutrons. Protons are positively charged and neutrons have no charge.
The electrons that move around the nucleus have a negative charge, they occupy shells.
Atoms have no charge (they're neutral)
Electrons always occupy shells.
1st shell - 2 electrons
2nd shell - 8 electrons
3rd shell - 8 electrons
When the outer shell is not full an atom will often react with another to fill it.
When elements react, atoms form chemical bonds to form compounds. The bonds often involve taking or sharing electrons.
Compounds formed between a non-metal and a metal consist of ions. Metals lose electrons forming positive ions and non-metals gain electrons forming negative ions. It's called ionic bonding.
Compounds formed from non-metals consists of molecules. It's called a covalent bond.
They can be small molecules or giant covalent structures.
Limestone's quarried from the ground, it's great to make into blocks to build with. It's made from calcium carbonate CaCO3. When it's heated it thermally decomposes to make calcium oxide and carbon dioxide.
When magnesium, copper, zinc and sodium carbonates are heated they decompose in the same way.
Calcium carbonate also reacts with acid to make calcium salt, carbon dioxide and water.
calcium carbonate = calcium oxide + carbon dioxide
CaCO3 = CaO + CO2
Uses of Limestone
Powdered limestone is heated in a kiln to make powdered clay or cement. Cement can be mixed with sand and water to create mortar. You can add calcium hydroxide to mortar.You can mix cement with sand and water and gravel to make concrete.
- huge holes permanently damage the environment
-blasting rocks with explsoives makes a lot of noise and dust in quiet areas - cment factories can cause breathing problems due to dust
-destroys the habitat of animals
-its transported in lorries causing noise and pollution
-waste material produces tips
Liestone provides things like: housing, roads, dyes, paint, medicines, neutralising acidic soil, neutralising acidity in rivers and lakes, neutralises sulfur dioxide, The quarry provides jobs, local improvements (transport, roads, recreation facilities).
Limestone is widely available and it's cheaper than granite or marble. And it's also easier to cut.
Extracting metals from Rocks
A metal ore is a rock which contains enough metal to make it worthwhile extreacting metal from it. Most metals need to be exctrated from their ores using a chemical reaction. A metal can be exctracted from its ore chemically (by reduction) or by electrolysis. Electrolysis can also be used to purify the exctracted metal.
Extracted chemically - by reduction
A metal can be extracted from its ore chemically by reduction using carbon. When an ore is reduced,oxygen is removed.
Less reactive metals (than carbon) are extracted by reduction.
Because carbon can only take the oxgen from something which is less less reactive than carbon itself is.
Iron oxide + carbon = iron + carbon dioxide
2Fe2O3 + 3C = 4Fe + 3CO2
Electrolysis is the breaking down or a substance using electricity. It requires a liqiud to conduct the electricty, called the electrolyte.
They are often metal salt solutions made from the ore. It has free ions allowing it to conduct electricity.
Electrons are rtaken away by the positive electrode and given away by the negative electrode.
Its a very expensive process and only happens with more reactive elements.
Properties or metals
-metals are strong, but they can be bent or hammered into different shapes
-they're great at conducting heat and electricity
some metals need to be protected because they can corrode when exposed to air and water.
Copper - is a good conductor or electricity so it's ideal for drawing into electrical wires. It's hard and strong but it can be bent, it doesn't reactwith water
Aluminium - it's corrosive resistant, has a low density it forms hard, strong alloys
Titanium - it's a low density metal, its very strong unlike aluminium and is also corrosive resistant.
Impurities - pure metals
Iron straight from a blast furnace is only 96% iron, the other 4% is impurities like carbon. The impure iron is used as cast iron. All the impurities are removed from the iron. This pure iron has a regualr arangement of indenticalatoms. The layers can slide over each other which makes it soft and bendy.
Most of the pure iron is changed into alloys called steels. Steels are formed by adding small amount of carbon.
Different elements have different sized atoms. When you add carbon to iron it upset the layers or pure iron making it more difficult to slide over. So the alloys are harder. Many metals used today are alloys.
e.g. copper, cupronickel, gold alloys and aluminium alloys.
Crude oil is a mixture of hydrocarbons. A mixture consists of two or more elements or compounds that aren't chemically bonded. Crude oil is a mixture of many different compounds, most of which are hydrocarbon molecules.
Hydrocarbons are basically fuels such as petrol and diesel, they're just made of carbon and hydrogen. There are no chemical bonds, this means that they keep all of their original properties.
The parts of a mixture can be separated. Crude oil can be separted into different fractions by fractional distillation.
Fractional distillation of crude oil
The fractioning column works continuously wth heatd crude oil piped in at the bottom. The vapourised oil rises up the column and the various fraction are constantly tapped off at different levels where they condense.
All of the fractions of crude oil called hydrocarbonsa re Alkanes. Alkanes are made up of chains of carbon atoms surrounded by hydrogen atoms. Different alkanes have different chains of length. The first four alkanes are methane, ethane, propane and butane.
Methane - CH4 (natural gas)
Ethane - C2H6
Propane - C3H8
Butane - C4H10
Carbon atoms form four bonds and hydrogen atoms only form one bond. The compound above are saturated. Alkanes have the general formula CnH2n+2
Crude oil as a fuel
Crude oil burns cleanly so it makes a good fuel. Most modern transport is fuelled by crude oil, it is also burned in power stations togenerate electricity. Crude oil fractions are often the cheapest and easiest to use for petrol and diesel.