AQA GCSE C2 condensed notes

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Chemistry C2 Condensed Notes
C2 Topic 1&2: Structure, Bonding and Properties
Simple particle theory is developed in this unit to include atomic
structure and bonding. The arrangement of electrons in atoms can be
used to explain what happens when elements react and how atoms join
together to form different types of substances.
Compounds are substances in which atoms of two or more elements are
chemically combined. Chemical bonding involves either transferring or
sharing electrons in the highest occupied energy levels (shells) of atoms
in order to achieve the electronic structure of a noble gas.
Substances that have simple molecular, giant ionic and giant covalent
structures have very different properties. Ionic, covalent and metallic
bonds are strong. However, the forces between molecules are weaker, eg
in carbon dioxide and iodine.
Ionic
Write formulae for ionic compounds from given
symbols and ionic charges. represent the
electronic structure of the ions in sodium
chloride, magnesium oxide and calcium
chloride as in the diagram. Ionic compounds
have regular structures (giant ionic lattices) in
which there are strong electrostatic forces in all
directions between oppositely charged ions. These compounds have
high melting points and high boiling points because of the large
amounts of energy needed to break the many strong bonds. When
atoms form chemical bonds by transferring electrons, they form ions.
Atoms that lose electrons become positively charged ions. Atoms that
gain electrons become negatively charged ions. Ions have the electronic
structure of a noble gas (Group 0).
The elements in Group 1 of the periodic table, the alkali metals, all react
with non-metal elements to form ionic compounds in which the metal
ion has a single positive charge.
The elements in Group 7 of the periodic table, the halogens, all react
with the alkali metals to form ionic compounds in which the halide ions
have a single negative charge. An ionic compound is a giant structure
of ions. These forces act in all directions in the lattice and this is called
ionic bonding. Candidates should be familiar with the structure of
sodium chloride but do not need to know the structures of other ionic
compounds. When melted or dissolved in water, ionic compounds
conduct electricity because the ions are free to move and carry the
current.
Covalent
Covalent - molecular
When atoms share pairs of
electrons, they form covalent
bonds. These bonds between atoms
are strong. Some covalently bonded
substances consist of simple

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H2, Cl2, O2, HCl, H2O, NH3 and CH4. Represent the
covalent bonds in molecules such as water, ammonia, hydrogen,
hydrogen chloride, methane and oxygen, and in giant structures such as
diamond and silicon dioxide, as shown in the diagram: Substances that
consist of simple molecules are gases, liquids or solids that have
relatively low melting points and boiling points. Substances that consist
of simple molecules have only weak forces between the molecules
(intermolecular forces).…read more

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Candidates should know that
conduction depends on the ability of electrons to move throughout the
metal. The layers of atoms in metals are able to slide over each other
and so metals can be bent and shaped. Alloys are usually made from
two or more different metals. The different sized atoms of the metals
distort the layers in the structure, making it more difficult for them to
slide over each other and so make alloys harder than pure metals.…read more

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C3 Topic 3: How Much?
Atoms can be represented as shown in this
example:
The relative masses of protons, neutrons and
electrons are:
The total number of protons and neutrons in an
atom is called its mass number.
Atoms of the same element can have different numbers of neutrons;
these atoms are called isotopes of that element.
The relative atomic mass of an element (Ar) compares the mass of atoms
of the element with the 12C isotope.…read more

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Candidates need only a basic
understanding of how GC-MS works, limited to:
different substances, carried by a gas, travel through a column packed with a
solid material at
different speeds, so that they become separated
the number of peaks on the output of a gas chromatograph shows the
number of compounds
present
the position of the peaks on the output indicates the retention time
a mass spectrometer can identify substances very quickly and accurately
and can detect very small quantities.…read more

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Energy
Chemical reactions involve energy transfers. Many chemical reactions
involve the release of energy. For other chemical reactions to occur,
energy must be supplied. When chemical reactions occur, energy is
transferred to or from the surroundings.
An exothermic reaction is one that transfers energy to the
surroundings. Examples of exothermic reactions include combustion,
many oxidation reactions and neutralisation. Everyday uses of
exothermic reactions include self-heating cans (eg for coffee) and hand
warmers.
An endothermic
reaction is one that
takes in energy from the
surroundings.…read more

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C2 Topic 5: Salts and Electrolysis
Soluble salts can be made from acids and insoluble salts can be made from
solutions of ions.
Select an appropriate method for making a salt, given appropriate
information.
The state symbols in equations are (s), ( l ) , (g) and (aq).…read more

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Electrolysis
Ionic compounds have many uses and can provide other substances.
Electrolysis is used to produce alkalis and elements such as aluminium,
chlorine and hydrogen. Oxidation­reduction reactions do not just
involve oxygen.
predict the products of electrolysing solutions of ions.
explain and evaluate processes that use the principles described in this
unit, including the use of electroplating.
When an ionic substance is melted or dissolved in water, the ions are
free to move about within the liquid or solution.…read more

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