C5 Chemicals of the Natural Environment

The earths atmosphere contains many gases- some are elements (Oxygen, Nitrogen and Argon), some are compounds (more than one type of atom joined together, Carbon Dioxide). Most of the gases in the atmosphere are molecular substances.

Molecular substances have lower melting and boiling points. This is because the forces of attraction between the molecules are very weak, you only need a little bit of energy to overcome these forces.

This means they are normally gases and liquids at room temperature. Pure molecular substances don't conduct electricity as they aren't charged (no free electrons or ions).

However, the atoms within the molecules are held together by very strong covalent bonds.

Most non-metal elements and most compounds formed from non-metal elements are molecular. H2O     CO2  

Covalent bonds - sharing electrons.

This way both atoms feel that they both have a full outer shell of electrons.

Each atom involved has the make enough covalent bonds to fill up its outer shell.

The atoms bond due to the electrostatic attraction between the positive nuclei and the negative electrons shared between them.

For example: Hydrogen needs one extra electron, so 2 hydrogen atoms share their outer electron so they have a full shell. This is covalent bonding.

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For example: Carbon dioxide needs 4, oxygen needs 2, so 2 double covalent bonds are formed. Double covalent bonding = 2 shared pairs of electrons. (Read page 41).

The earths hydrosphere consists of all the water in the oceans, seas, lakes, rivers, puddles etc... It also contains any compounds that are dissolved in the water. Many of theses compounds are ionic called salts e.g. Sodium Chloride (NaCl), Magnesium Chloride (MgCl2) and Potassium Bromide (KBr).

Solid ionic compounds form crystals made up of charged particles (ions).

Ions with opposite charges are strongly attracted to one another due to strong forces of attraction. This forms a regular lattice.

Very strong chemical bonds called ionic bonds, so it takes lots of energy to overcome these forces so high boiling and melting points.

They conduct electricity when dissolved or molten as ions separate and are free to move. This means they can carry an electric current. When ionic compounds are solid, the ions aren't free to move so no current can pass through and they cannot conduct electricity.

The earths Lithosphere is made up of a mixture minerals and consists of the crust and part of the mantle below it. The main elements in the Lithosphere are Silicon, Oxygen and Aluminium. Most of the oxygen and silicon exist as the compound silicon oxide.

Different rocks contain different minerals and elements. Limestone contains lots of calcium and sandstone contains lots of silicon dioxide.

Silicon dioxide (sand and is also found in quartz and granite) forms a giant covalent structure which contains no charged particles and is very hard.

Gian covalent structures have high melting and boiling points, they are usually insoluble and therefore don't conduct electricity.

Some minerals are very valuable gemstanes as they are very rare.

Gemstones are very hard. This is due to their giant covalent structures.

All living things are formed from compounds made up of the same basic elements.

These main elements are: Carbon, Hydrogen, Oxygen, Nitrogen ans small amounts of Phosphorus and Sulfur. These make up molecules vital for life- Carbohydrates, Proteins, Fats and DNA.

DNA- Phosphorus and Nitrogen.

Proteins- Nitrogen and Sulfur.

Fats/ Carbohydrates- Carbon, Hydrogen and Oxygen (fats contain a greater percentage of Carbon).

You can find formulas by counting elements in diagrams.

Elements are constantly moving between the different spheres, so flow charts can be used to summarise chemical changes between the spheres (read page 44).

Rocks are made of minerals (solid elements and compounds). Metal ores are rocks that contain varying amounts of minerals from which metals can be extracted.

The ore can be oxide of the metal e.g. iron ore is called haemate and copper ore is called chalcopyrite.

For some metals, large amounts of ore is needed to be mined to get only a small percentage of valuable minerals e.g. copper mining.

More reactive metals are harder to get.

A few unreactive metals like gold are found in the earth as a metal rather than a compound. Most metals need to be extracted from their ores using a chemical reaction. Really reactive metals are hard to extract e.g. sodium- so it took longer to discover.

Some metals can be extracted by reduction with carbon. When an ore is reduced, oxygen is removed from it.

When a metal oxide loses it's oxygen, it is reduced. The carbon gains the oxygen and it is oxidised. If the metal is more reactive than the carbon, electrolysis is used- below, reduction is used. (Read bottom of page 45).

Electrolysis- splitting up with electricity and the decomposition of a substance using electricity.

A liquid is needed to conduct the electricity. This is the electrolyte (free ions dissolved in water or molten ionic compounds).

The free ions conduct the electricity and for an electrical circuit to be complete there needs to be a flow of electrons.

In electrolysis, electrons are taken away from ions at the positive electrode and given to other ions at the negative electrode. As ions gain or lose electrons they become atoms or molecules.

Electrolysis removes aluminium from its ore (bauxite). Molten aluminium oxide contains free ions- so it conducts electricity.

The positive Al3+ ions are attracted to the negative electrode where they pick up 3 electrons and turn into neutral aluminium atoms. The negative O2- ions are attracted to the positive electrode where they each lose 2 electrons. The neutral oxygen atoms will then combine to form O2 molecules. (Look at picture on back).

Metal properties are all due to the sea of free electrons.

Metals consist of a giant structure.

Metallic bonds involve the ell important free electrons which produce all the properties of metals.

These free electrons come from the outer shell of every metal atom in the structure. The positively charged metal ions are held together by these electrons.

They're good conductors of heat and electricity due to the free electrons carrying both heat and electrical current through the material e.g. saucepan bases.

Most metals are strong and malleable (high tensile strength) good for car bodies and bridges.

They generally have high melting and boiling points as metallic bonds are very strong so it takes a lot of energy to break them.

Ores are finite resources- there's only a limited amount and eventually they'll run out.

You have to balance the social, economic and environmental effects of mining for ores.

Metal mining is good as useful products can be made, provides jobs and brings money to the area. BUT, its bad for the environment.

Recycling metals is important.

Mining and extracting metals takes lots of energy, most of which comes from burning fossil fuels.

Fossil fuels are running out so we need to conserve them. Burning them also contributes to acid rain, global warming and climate change.

Recycling only uses a small fraction of energy, so it saves money too. Recycling conserves finite resources and cuts down on the amount of rubbish going to landfill. Landfill takes up space and pollutes the environment.