C5 revision

Atmosphere:
The layer of gas surrounding the earth. Elements include nitrogen, oxygen and argon. Compounds include carbon dioxide and water vapour.

Hydrosphere:
Mostly made up of water and some dissolved compounds.

Lithosphere:
The rigid outer layer of earth; crust and part of the mantle. Contains a mixture of minerals e.g. Silicon dioxide. Abundance of elements e.g. silicon, oxygen and aluminium.

Nitrogen 78%
Oxygen 21%
Argon 1%
Carbon dioxide 0.04%
Water vapour varies
Gases in the air are at 20 degrees Celsius (they have low boiling points due to weak intermolecular forces)

In covalently bonded molecule (they share electrons), there is electrostatic attraction between each positively charged nucleus and the shared pain of negatively charged electrons.

The elements in the atmosphere are all covalently bonded.

Pure molecular compounds do not conduct electricity because their molecules are not charged.

If an element is abundant is means it is extremely common to find.

Oxygen is the most abundant element in the lithosphere (455000ppm)

Silicon is the second most abundant element in the atmosphere (272000ppm)

Aluminium is the third most abundant element in the atmosphere (83000ppm)

Diamond and graphite are both minerals made from pure carbon.

In a diamond, the carbon atoms are covalently bonded with four other carbon atoms, in a tetrahedral structure. This means diamonds are strong and hard, because of the strong covalent bonds. Has a high melting point and are insoluble in water.

In graphite, each carbon atom is covalently bonded with three other carbon atoms arranged in sheets so they can slide over each other. As each atom is only bonded to three other atoms that means there is spare electrons that can move in between the layers of atoms. These are called delocalised electrons. This means graphite can conduct electricity as the electrons can flow and carry a charge. Graphite can be used as a dry lubricant.

Silicon and oxygen in lithosphere is presented as silicon dioxide SiO2.

Silicon dioxide is a giant covalent structure, similar to diamonds.

Properties include:

• hard
• high melting point
• electrical insulator
• insoluble in water

Seawater in hydrosphere us 'salty' because it contains dissolved ionic compounds called salts.

Sodium chlorides negative and positive ions are electrostatically attracted to form a giant 3D crystal lattice.

Properties of ionic compounds:

• high melting points and high boiling points (ions are held together by strong forces of attraction)
• do not conduct electricity (ions are fixed in place and cannot move)
• do conduct electricity when molten or dissolved (ions are free to move)

Calcium ions combine with carbonate ions to form an insoluble ionic compound called calcium carbonate or limestone (precipitate).

Positive metal ions can be identified in a solution by adding sodium hydroxide solution (NaOH) and observing colour of the precipitate.

An hydroxide ion has a single negative charge (OH-)

Negative (non metal) ions will react with other aqueous ions to form insoluble solutions.

Ores:
Ores are rocks containing varying amounts of minerals, from which metals can be extracted.

Sometimes very large amounts of ores are needed to get a small percentage of the mineral e.g. Copper.

Method of extraction depends on how reactive the metal is.

Metals that are less reactive than carbon can be extracted from their oxides by heating with carbon:

• the metal oxide is reduced
• the carbon is oxidised

E.g.
Zinc oxide + carbon -> zinc + carbon dioxide

RFM- relative formula mass (total mass of the atoms in a compound)
Add up the relative atomic masses to find the RFM.

RFM of CO2 =
12+16+16= 44

Calculating a metals mass:
1. Write down formula.
2. Work out RFM.
3. Work out percentage mass of the metal by diving the RAM (relative atomic mass) of the metal by the RFM of the metal oxide then multiply answer by 100.
4. Work out the mass of metal by dividing the percentage by the amount of metal used the multiply answer by 100.

Example: find mass of Zn that can be extracted from 100g of ZnO.
1.ZnO
2. Relative formula mass = 65+ 16= 81
3. Percentage of zinc present= RAM of Zn/RFM of ZnO= 65/81*100= 80%
4. In 100g of ZnO, there will be 80/100*100= 100g of Zn.

Electrolysis: the breaking down of an electrolyte using an electric current.

This is used to extract reactive metals from their ores because they are too reactive to be heated by carbon.

Ionic compounds conduct electricity when molten or dissolved in solution. Ions are free to move through liquid. The electrostatic forces between the charged ions in the crystal lattice are broken down and the ions are free to move.

When a direct current is passed through a molten ionic compound:

• positively charged ions are attracted towards the negative electrode (cathode)
• negatively charged ions are attracted towards the positive electrode (anode)

When ions get to oppositely charged electrodes they are discharged- they lose their charge.
Can be written as half equations. Write what is happening at each electrode. E.g.
2Br(-) -> Br2 +2e(-)
Pb(2+) + 2e(-) -> Pb

1. Aluminium ore (bauxite) is purified to leave aluminium oxide.
2. Aluminium oxide is mixed with cryolite (a compound of aluminium) to lower its melting point.
3. The mixture of aluminium oxide and cryolite is melted, so ions can move.
4. When a current is passed through the molten mixture, positively charged aluminium ions move toward the negative electrode- aluminium is formed.
5. Negatively charged oxide ions move towards the positive electrode- oxygen is formed.

At the negative electrode aluminium ions gain electrons to become neutral atoms.
Al(3+) + 3e(-) -> Al

At positive electrode oxygen ions lose electrons to become neutral atoms.
2O(2-) - 4e(-) -> O2

A life cycle assessment helps scientists to make decisions about which method of extraction causes the least environmental damage.

Stage of life cycle - Process - Environmental impact
Making the material from Mining. Rocked wasted. Scar on landscape.
natural raw materials. Air and noise pollution.

Processing Pollutant caused by transportation.
Energy usage. Electrolysis uses more
energy than reduction.

Manufacture Manufacturing. Energy usage in processing and
metal products. transportation

Use. Transport to shops/home Pollutants. Energy usage.
Running the product.
Disposal. Reuse, recycle, throw. No impact. Less energy usage. Land
away. fill sites remove wildlife habitats. Ugly

A metal has a giant structure of ions held together by a strong force of attraction called the metallic bond.

Metals:

• are strong (ions are closely packed in a lattic structure)
• have high melting points (a lot of energy is needed to break the bonds)
• malleable (can be beaten into shape as the layers of metal ions can slide over each other)
• conductors of electricity (electrons are free to move throughout the structure. When voltage is applied the electrons move the metal all in one direction).

In a metal the positively charged metal ions are held together by a 'sea' of electrons.

Titanium is strong and is used for replacement hip joints and submarines.
Aluminium is malleable and is used for drink cans.
Iron has a high melting point and is used for making saucepans.
Copper is an excellent conductor of electricity and is used for cables and electrical switches.