Chemistry AQA Higher Higher Tier Full Revision Notes

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Chemistry Revision
Atoms consist of electrons surrounding a nucleus that contains protons and neutrons. Neutrons are neutral, but
protons and electrons are electrically charged: protons have a relative charge of +1 and electrons have a
relative charge of -1.
Atoms and elements
All substances are made of tiny particles called atoms. An element is a substance that is made of one sort of atom.
Atomic structure
An atom has a small central nucleus made up of smaller sub-atomic particles
called protons and neutrons. The nucleus is surrounded by even smaller sub-atomic
particles called electrons.
Protons and electrons have an electrical charge. Both have the same size of
electrical charge, but the proton is positive and the electron negative. Neutrons
are neutral.
A summary of the electrical charges in sub-atomic particles
The number of electrons in an atom is equal to the number of protons in its nucleus.
This means atoms have no overall electrical charge.
Full chemical symbols
The full chemical symbol for an element shows its mass number at the top, and its atomic number at
the bottom.
This symbol tells you that the chlorine atom has 17 protons. It will also have 17 electrons, because
the number of protons and electrons in an atom is the same.
The symbol also tells you that the total number of protons and neutrons in the chlorine atom is 35. Note that you
can work out the number of neutrons from the mass number and atomic number. In this example, it is 35 ­ 17 = 18
neutrons.
Writing an electronic structure
***JUST REMEMBER 2, 8, 8, 2*******
Reactions and compounds
New substances are formed by chemical reactions. When elements react together to form compounds their atoms
join to other atoms using chemical bonds. For example, iron and sulphur react together to form a compound called
iron sulphide.
Compounds usually have different properties from the elements they contain.
Covalent bonds
Compounds formed from non-metals consist of molecules. The atoms in a molecule are joined together by
covalent bonds. These bonds form when atoms share pairs of electrons.
Copper and oxygen reaction: getting a balanced equation
Take a look at this word equation for the reaction:
Copper + oxygen copper oxide
If we just replace the words shown above by the correct chemical formulas, we will get an unbalanced equation,
as shown here:

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Cu + O2 CuO
CHO, first carbon then hydrogen and then oxygen
Here is the balanced symbol equation:
2Cu + O2 2CuO
Calcium Carbonate
Limestone is mainly calcium carbonate, CaCO3, which when heated breaks down to form calcium oxide and
carbon dioxide. Calcium oxide reacts with water to produce calcium hydroxide. Limestone and its products
have many uses, including being used to make cement, mortar and concrete.
Thermal decomposition
Calcium carbonate breaks down when heated strongly. This reaction is called thermal decomposition.…read more

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The Earth's crust contains metals and metal compounds , but when found in the Earth these are often mixed with
other substances. To become useful, the metals have to be extracted from whatever they are mixed with. A metal
ore is a rock containing a metal, or a metal compound, in high enough concentration to make it economic to extract
the metal. Ores are mined.
Reactivity and extraction method
Metals are produced when metal oxides are reduced (have their oxygen removed).…read more

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Alkanes
Most of the compounds in crude oil are hydrocarbons. These are compounds that contain hydrogen and carbon
atoms only, joined together by chemical bonds called covalent bonds. There are different types of hydrocarbon, but
most of the ones in crude oil are Alkanes.
The Alkanes are a family of hydrocarbons that share the same general formula. This is:
CnH2n+2
The general formula means that the number of hydrogen atoms in an Alkane is double the number of carbon
atoms, plus two.…read more

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Acidic oxides
Carbon dioxide dissolves in water in the atmosphere to form a weakly acidic solution. This means that
rainwater is naturally slightly acidic. However, some of the products from burning fuels make rainwater more acidic
than normal. This is acid rain.
Acid rain reacts with metals and rocks such as limestone, causing damage to buildings and statues. Acid rain also
makes rivers and lakes too acidic for some aquatic life to survive.
Sulphur dioxide
Coal and most hydrocarbon fuels naturally contain some Sulphur compounds.…read more

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