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WJEC
CBAC



AS/A LEVEL
GCE in Chemistry

REVISION AID

UNIT 1

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AS



UNIT CH1 ­ Controlling and Using Chemical Changes (in order to make things,
produce energy and solve environmental problems)




Preamble
This unit begins with some important fundamental ideas about atoms and the use of
the mole concept in calculations.

Three key principles governing chemical change are then studied, viz.…

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UNIT CH1 Controlling and Using Chemical Changes (in order to make things,
produce energy and solve environmental problems)


TOPIC 1

1.1 Basic ideas about atoms

1.2 Chemical calculations

TOPIC 2

2.1 Chemical eqilibria and acid-base reactions

2.2 Energetics

2.3 Kinetics

TOPIC 3

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1.1 Basic ideas about atoms

Topic 1.1 (a)

Learning Outcome: Describe electrons, protons and neutrons in terms of their
relative charges and masses, and the distribution of charges and masses within
atoms.

Atomic Structure.

Atoms are made up of three fundamental particles, the proton, the neutron and the
electron.

electrons…

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Topic 1.1 (b)

Learning Outcome: understand the terms atomic number, mass number and
isotope, and the connection between atomic numbers and mass numbers.


The number of protons in the nucleus of an atom is called the atomic number (Z).
Each element has its own atomic number.
For example hydrogen has…

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Topic 1.1 (c)

Learning Outcome: deduce, given atomic and mass numbers, the numbers of
protons, neutrons and electrons in specified isotopes;


35 37
Taking the isotopes above, 17 Cl and 17 Cl , we can deduce the numbers of electrons,

protons and neutrons in each neutral atom.

mass number(A) =…

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Topic 1.1 (e)

Learning Outcome: describe the nature of alpha () and beta () particles and of
gamma () radiation and recall their behaviour in electrical fields and their relative
penetrative powers.

Radioactive isotopes
Some isotopes are unstable; these are usually, but not always, heavy nuclei like
those of uranium…

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Topic 1.1 (f)

Learning Outcome: describe and explain the changes in mass number and atomic
number resulting from alpha () and beta () emission

It is important to note that these radiations come from the nucleus of the atom.
This means that alpha () and beta () radioactive emissions result…

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Topic 1.1 (g)

Learning Outcome: describe the adverse consequences for living cells of exposure
to - radiation and to - and - emitters;

We all receive radiation which is called background radiation, arising from naturally
occurring radioactive sources, man-made radiation and radiation reaching the Earth
from space.

APPROXIMATE TOTAL YEARLY…

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It is known that exposure to radiation can cause cell mutation leading to carcinomas
and to forms of leukaemia. Even small increases in the background level of radiation
may have significant effects on the population as a whole. This is because the
probability for cell mutation is higher when applied…

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