Chemistry GCSE (1)

Science A GCSE - Chemistry

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ATOMS, ELEMENTS AND COMPOUNDS

All substances are made from atoms.

Substances made of only one atom are called elements e.g. silver, gold, oxygen. 

Most substances are made up of more than one atom, these are called compounds.

Every atom has a nucleus in the middle, surrounded by electrons.

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ATOMIC STRUCTURE

NEUTRONS = mass number - atomic number

MASS NUMBER = protons + neutrons

PROTONS = atomic number (bottom number)

ELECTRONS = PROTONS

Protons = positive = +1

Neutrons = neutral = 0

Electrons = -1

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ELECTRONS IN ATOMS

Electronic structure:

First shell = up to 2

Every other shell = up to 8

Noble gases

Group 0 of periodic table

Unreactive

All have 8 electrons in outermost shell


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LIMESTONE

Limestone is made of calcium carbonate.

Calcium carbonate = CaCO3

When heatedcalcium carbonate breaks down to make calcium oxide and carbon dioxide - thermal decomposition.

Testing for carbon dioxide = 

calcium hydroxide + carbon dioxide --> calcium carbonate + water

    (limewater)                                             (precipitate - cloudy)

     Ca(OH)2             +          CO2           -->           CaCO3            +  H2O      



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LIMESTONE REACTION CYCLE

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EXTRACTING METALS

Displacement reaction = one metal is more reactive than the other.

e.g. magnesium + zinc oxide --> magnesium oxide + zinc (because magnesium is more reactive than zinc)

Smelting = heating a metal ore in order to extract its metal.

Bioleaching = using bacteria to extract copper.

Phytomining = using plants to produce pure copper.

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