Atoms contain three sub-atomic particles called protons, neutronsand electrons.The protons and neutrons are found in the nucleus at the centre of the atom. The electrons are arranged in shells around the nucleus.

Atomic number and mass number

The number of protons in the nucleus of an atom is called its atomic number:

• the atoms of a particular element all have the same number of protons
• the atoms of different elements have different numbers of protons

The total number of protons and neutrons in an atom is called itsmass number.

Electron shells

Electrons are arranged in different shells around the nucleus. Each successive shell can only hold a certain number of electrons.

The innermost shell is filled first. This shell can contain a maximum oftwo electrons. The second shell can hold a maximum of eightelectrons. When this is filled, electrons go into the third shell, which also holds a maximum of eight electrons. Then the fourth shell begins to fill.

• The presence of the C=C double bond allows alkenes to react in ways that alkanes cannot. This allows us to tell alkenes apart from alkanes using a simple chemical test.
• Bromine water is an orange solution of bromine. It becomes colourless when it is shaken with an alkene. Alkenes can decolourise bromine water, but alkanes cannot. The slideshow shows this process.

Combustion

When a substance burns, it reacts with oxygen. This is known as combustion. All combustion reactions are exothermic because they release energy, eg heat energy is given out when methane is burned in a bunsen burner.

• The earth consists of a core, mantle and crust.
• scientists once thought that the features of the earth's surface were the result of the shrinking of the crust as the earth cooled down following its formation.
• The earth's crust and the upper part of the mantle are cracked into a number of large pieces called tectonic plates.
• Convection currents within the earth's mantle, driven by heat released by natural radioactive processes, cause the plates to move at relative speeds of a few cm per year.
• The movements can be sudden and disaterous.
• earthquakes and/or volcanic eruptions occur at the boundaries between tectonic plates.

Early atmosphere

• when the planet was formed 4.5 billion years ago, there was no atmosphere.
• during the first billion years volcanoes released carbon dioxide, water vapour, methane and ammonia into the atmosphere.
• There would have been little or no oxygen.

atmosphere today

• 78%nitrogen
• 21% oxygen
• 0.9% argon
• 0.04% carbon dioxide

formation of oceans

• As the planet cooled, some of the water vapour condensed to form oceans
• mst of the carbon dioxide dissolved in the oceans and became locked in sedimentary rocks and fossil fuels. 

• Sulfur dioxide and carbon monoxide are two of the gases produced when fossil fuels burn.
• Carbon monoxide, CO, is produced when fuels burn in a limited amount of air. It is a colourless, odourless and tasteless gas. Carbon monoxide passes into the red blood cells after breathing it in. It binds more strongly to haemoglobin than oxygen does, so the blood will be able to carry less oxygen than it should. This can cause tiredness, unconsciousness and even death.
• Fossil fuels naturally contain sulfur compounds. These produce sulfur dioxide, a gas with a sharp, choking smell, when the fuel is burned. When sulfur dioxide dissolves in water droplets in clouds, it makes the rain more acidic than normal. This is called acid rain
• carbon dioxide is given off when burning fossil fuels, this contributes to global warming because it adds to the atmosphere. carbon dioxide is a greenhouse gas and the build up of greenhouse gases in the earths atmosphere causes the atmosphere to heat up.

1. 1) Sunlight passes through the Earth’s atmosphere.
2. 2)The ground warms up and heat is emitted from the Earth’s surface.
3. 3)Some heat escapes into space but some is absorbed by greenhouse gases. It is re-emitted and does not escape.
4. 4)The Earth’s atmosphere warms up

• Vegetable oils are natural oils found in seeds, nuts and some fruit. These oils can be extracted. The plant material is crushed and pressed to squeeze the oil out. Olive oil is obtained this way. Sometimes the oil is more difficult to extract and has to be dissolved in a solvent. Once the oil is dissolved, the solvent is removed by distillation, and impurities such as water are also removed, to leave pure vegetable oil. Sunflower oil is obtained in this way

vegetable oils have higher boiling points than water. This means that foods can be cooked or fried at higher temperatures than they can be cooked or boiled in water. Food cooked in vegetable oils:

• cook faster than if they were boiled
• have different flavours than if they were boiled.

However, vegetable oils are a source of energy in the diet. Food cooked in vegetable oils releases more energy when it is eaten than food cooked in water. This can have an impact on our health. For example, people who eat a lot of fried food may become 

Vegetable oils do not dissolve in water. If oil and water are shaken together, tiny droplets of one liquid spread through the other liquid, forming a mixture called an emulsion.

Emulsions are thicker (more viscous) than the oil or water they contain. This makes them useful in foods such as salad dressings and ice cream. Emulsions are also used in cosmetics and paints. There are two main types of emulsion:

If an emulsion is left to stand, eventually a layer of oil will form on the surface of the water. Emulsifiers are substances that stabilise emulsions, stopping them separating out. Egg yolk contains a natural emulsifier. Mayonnaise is a stable emulsion of vegetable oil and vinegar with egg yolk

Emulsifier molecules have two different ends:

Lecithin is an emulsifier commonly used in foods. It is obtained from oil seeds and is a mixture of different substances. A molecular model of one of these substances is seen in the diagram.

The hydrophilic 'head' dissolves in the water and the hydrophobic 'tail' dissolves in the oil. In this way, the water and oil droplets become unable to separate out

Saturated and unsaturated fats and oils

The fatty acids in some vegetable oils are saturated: they only have single bonds between their carbon atoms. Saturated oils tend to be solid at room temperature, and are sometimes called vegetable fats instead of vegetable oils. Lard is an example of a saturated oil.

The fatty acids in some vegetable oils are unsaturated: they have double bonds between some of their carbon atoms. Unsaturated oils tend to be liquid at room temperature, and are useful for frying food. They can be divided into two categories:

monounsaturated fats have one double bond in each fatty acid

polyunsaturated fats have many double bonds.

Unsaturated fats are thought to be a healthier option in the diet than saturated fats.

• veg oils that are unsaturated contain double carbon=carbon bonds (can be detected with bromine water)
• unsaturated veg oils can be hardened by reacting them with hydrogen in the presence of a nickel catalyst at about 60 degrees.

desructive plate boundary

• A destructive plate boundary is sometimes called a convergent or tensional plate margin. This occurs when oceanic and continental plates move together. The oceanic plate is forced under the lighter continental plate. Friction causes melting of the oceanic plate and may trigger earthquakes. Magma rises up through cracks and erupts onto the surface.

constructive plate boundary

• A constructive plate boundary, sometimes called a divergent plate margin, occurs when plates move apart. Volcanoes are formed as magma wells up to fill the gap, and eventually new crust is formed.

conservative plate boundary

• A conservative plate boundary, sometimes called a transform plate margin, occurs where plates slide past each other in opposite directions, or in the same direction but at different speeds.Friction is eventually overcome and the plates slip past in a sudden movement. The shockwaves created produce an earthquake