# AS Science Unit 2 Module 1

Key terms and deifinitions for AS science

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## The Atmosphere

Troposphere: The lowest layer in the Earth's atmosphere extending up to around 15km from the Earth's surface.

Tropopause: The boundary between the troposphere and the stratosphere.

Stratosphere: The layer in the Earth's atmosphere between 15 and 50km from the Earth's surface.

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## Forces

Pressure: The force acting on a fixed area. E.g. the force exerted on 1m2 of air. Measured in Newtons (N) also known as Pascals (Pa).

Coreolis Effect: A force caused by the rotation of the Earth which deflects moving air as it moves from high to low pressure.

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## Bonds

Molecule: A particle made up of two or more atoms bonded together by covalent bonds.

Covalent Bond: A type of bond in which atoms share electrons. It is often represented by a single line in structural formulae.

Electronegativity: A measure of how strongly an atom attracts electrons in a covalent bond. The higher the electronegativity, the stronger the attraction for electrons.

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## Water

Specific Heat Capacity: The amount of energy required to raise the temperature of 1g (1cm3) of water by 1oC (1K).

Density: The mass of a fixed volume of a substance (density=mass/volume).

Thermohaline Circulation: Sinking or rising of water caused by differences in temperature and concentration of dissolved salts (particularly halides).

Scientific Model: An idea that allows us to create explanations of how we think some part of the world works. A model may be based on mathematical patterns and can be used to make precise predictions about the effect of changes in conditions.

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Radiocarbon Dating: A way of estimating the age of material that was once alive. It relies on the fact that the radioactivity of the C-14 isotope falls in a regular way after the death of an organism.

Isotopes: Different forms of the same type of atom that have the same atomic number but different mass numbers.

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## Greenhouse Effect

Greenhouse Effect: The warming of the atmosphere caused by the ability of some gases to trap infrared radiation emitted by the Earth.

Greenhouse Gas: A gas which can absorb and trap infrared radiation emitted by the Earth. E.g. carbon dioxide, methane, water vapour and clorofluorocarbons.

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