AQA C2 Revision Notes

brief revision notes for AQA GCSE C2

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Chemistry Unit 2 Revision
Atomic Structure
In the nucleus of atoms there are protons and neutrons. Around the
nucleus there are electrons which have a negative charge. In the
periodic table, atoms are arranged in order of their atomic number.
The Arrangement of Electrons in Atoms
The electrons in an atom are arranged in an atom are arranged around
the nucleus in shells or energy levels. The electrons further away from
the nucleus have more energy than those close to the nucleus. As you
go across a group of the periodic table each element has one more
electron than the previous element. All elements in the same period
have the same number of electrons in their outer shell.
Chemical Bonding
When two substances react together they make a new substance and it
is difficult to separate them. Some atoms react by sharing electrons ­
we call this covalent bonding. Other atoms react by gaining or losing
electrons ­ we call this ionic bonding. When atoms react in this way
they tend to get the electronic structure of a noble gas.
Covalent Bonding
When non-metal atoms react together they tend to produce covalent
bonds. The atoms in these bonds are held together by shared
electrons. Most substances held together by covalent bonds consist of
molecules but a few have giant structures.
Bonding in Metals
Metals also have giant structures. The atoms in these are held together
by the positive energy levels of the metal atoms. The outer ions that
this produces are held together by electrostatic forces. The electrons
in metals are free to move throughout the structure.
Laura Gill "Unit 2 Notes"

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Ionic Compounds
Ionic compounds have high melting points and boiling points because
of the strong electrostatic forces of attraction between oppositely
charged ions in the giant lattice. Ionic compounds will conduct
electricity when molten or in solution because the ions are able to
move freely.
Simple Molecules
Non-metals react to form molecules which are held together by strong
bonds. These hold the atoms together very strongly. The forces
between molecules are relatively week so they have low melting and
boiling points.…read more

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Masses of Atoms and Moles
We measure the masses of atoms by comparing them to the mass of
one atom of carbon-12. The relative atomic mass of an element is
usually almost the same as its mass number. We calculate the relative
formula mass of a compound from the relative atomic masses of the
elements in it.…read more

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Ammonia is an important chemical used for making fertilisers. The raw
materials are nitrogen from the air and hydrogen from natural gas.
These are reacted at about 450°C and 200 atmospheres pressure using
an iron catalyst. Ammonia is removed from the mixture before it can
break down into the reactants again by liquidising the gas.
How Fast?
Measuring how the rate at which reactants are used up or products are
made are two ways of measuring the rate of a chemical reaction.…read more

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A catalyst increases the rate of a chemical reaction. It does this by
reducing the activation energy needed for the reaction. This means
that more particles have enough energy to react.
Endothermic and Exothermic Reactions
Chemical reactions involve energy changes as bonds are made and
broken. When a chemical reaction releases energy we say that it is an
exothermic reaction. Two important examples of this kind of reaction
are neutralisation and respiration.…read more

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Changes at the Electrode
During electrolysis ions move towards the electrodes. At the cathode
(-) positively charged ions are reduced and gain electrons. At the anode
(+) negatively charged ions are oxidised and lose electrons. When
electrolysis is carried out in water, the less reactive element is usually
Electrolysing Brine
When we pass an electric current through brine we make hydrogen
gas, chlorine gas and sodium hydroxide solution. These products are
also used to make chlorine solution (bleach) and hydrochloric acid.…read more

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Salts can be made by reacting acids with metals, when hydrogen gas is
formed along with the salt. They can also be made by reacting acids
with insoluble bases, when water is formed as well as the salt.
Making Salts from Solutions
We can make salts by reacting an acid and an alkali. This makes the
salt and water. We can also make insoluble salts by reacting two
soluble salts together. We call this a precipitation reaction because the
salt is formed as a solid.…read more



Thanks so much! They are really helpful! Was wondering if you had any for C1& 3 as well?

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