AQA GCSE Chemistry Sample Pages

32 Pages·2015·2.45 MB·English

This title has been selected for
AQA’s approval process
AQA
GCSE
Chemistry
Richard Grime
Nora Henry
SAMPLE
CHAPTER
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AQA
GCSE
Chemistry
Richard Grime
Nora Henry
iiiiii
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Photo credits
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Contents
Getting the most from this book
1 Atomic structure and the periodic table 2
2 Bonding, structure and the properties of matter
3 Quantitative chemistry
4 Chemical changes
5 Energy changes
6 The rate and extent of chemical change
7 Organic chemistry
8 Chemical analysis
9 Chemistry of the atmosphere
10 Using the Earth’s resources
Formulae and equations
Index
Appendix
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1
Atomic structure and the

periodic table
Until you reached GCSE, Chemistry was
studied at the particle level. In order to
take chemistry further, you now need to
understand what is inside atoms. The
elements in the periodic table are
ordered by what is inside their atoms. An
understanding of the periodic table allows
you to explain and/or work out a lot of
chemistry even if you have never studied it.
e
g This chapter covers specifi cation points
a
r 1.1a to 1.3b and is called Atomic
e
v
o structure and the periodic table.
c

n
o It covers the structure of atoms,
ti
a reactions of elements, the periodic table
c
fi and mixtures.
ci
e
p
S
2
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Structure of atoms
Previously you could have learned:
e
g
d
e › Elements are made of particles called atoms.
l
w
› Elements are substances containing only one type of atom –
o
n this means they cannot be broken down into simpler
k
substances.

r
o › Each element has its own symbol and is listed in the periodic
i
Pr table.
› Elements are either metals or non-metals.
› Compounds are substances made from atoms of different
elements joined together.
› Compounds have different properties to the elements from
which they are made.
› Compounds are difficult to break back down into their elements.
› Substances in mixtures are not chemically joined to each other.
› Substances in mixtures can be separated easily by a range of
techniques.
Test yourself on prior knowledge
1 What is an element?
2 What is a compound?
3 Why do compounds have different properties from the elements
from which they are made?
4 List some differences between metals and non-metals.
5 Why is it easy to separate the substances in a mixture but not to
break apart a compound?
6 Name four methods of separating mixtures.
Structure of atoms
● Protons, neutrons and electrons
TIP
Remember that: Atoms are the smallest part of an element that can exist. Atoms are made
protons are positive up of smaller particles called protons, neutrons and electrons. The table
neutrons are neutral
below shows the relative mass and electric charge of these particles. The
leaving electrons as negative
mass is given relative to the mass of a proton. Protons and neutrons have
the same mass as each other while electrons are much lighter.
TIP
TThhee cchhaarrggee ooff aa pprroottoonn ccaann bbee wwrriitttteenn Proton Neutron Electron
as + or +1. The charge of an electron
Relative mass 1 1 very small
can be written as −1 or −.
Relative charge +1 0 −1
KEY TERM ● The structure of atoms
Atom TThhee ssmmaalllleesstt ppaarrtt ooff aann eelleemmeenntt
Atoms are very small. Typical atoms have a radius of about 0.1 nm
that can exist. A particle with no electric
charge made up of a nucleus containing (0.0000000001 m, that is 1 × 10−10 m). Atoms have a central nucleus which
protons and neutrons surrounded by contains protons and neutrons. The nucleus is surrounded by electrons. The
electrons in energy levels. electrons move around the nucleus in energy levels or shells.
3
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e TIP nucleus containing Key
abl 1 nm = 1 × 10−9 mm ((00..000000 000000 000011 mm)) protons and neutrons proton
t neutron

c
di electron
o TIP
eri TThhee SSII uunniittss ffoorr lleennggtthh aarree mmeettrreess ((mm))..
p

e
electrons move
h
t around the

d KEY TERMS nucleus in energy
n
a Proton Positively charged particle 3D diagram levels (shells) 2D diagram

e
r found inside the nucleus of atoms.
u
The nucleus is tiny compared to the size of the atom as a whole. The
t
c Neutron Neutral particle found inside
u radius of the nucleus is less than 1/10000th of that of the atom
r the nucleus of atoms.
t (1 × 10−14 m). This difference in size between a nucleus and an atom
s
Electron Negatively charged particle
c is equivalent to a pea placed in the middle of a football pitch.
mi found in energy levels (shells) outside
o the nucleus inside atoms.
t
A
Nucleus Central part of an atom

1
containing protons and neutrons.
Energy level (shell) The region an
electron occupies outside the nucleus
inside an atom.

▲ Figure 1.1 The size of the nucleus compared to the atom is like a pea compared to
a football pitch.
The nucleus contains protons and neutrons. These are much heavier
than electrons. This means that most of the mass of the atom is
contained in the tiny nucleus in the middle.
Test yourself
1 The radius of a hydrogen atom is 2.5 × 10−11 m. Write this in
nanometres.
2 Carbon atoms have a radius of 0.070 nm. Write this in standard form in the
units of metres.
3 The radius of a chlorine atom is 1 × 10−10 m and the radius of a silicon
atom is 0.060 nm. Which atom is bigger?
4 Sodium atoms have a radius of 0.180 nm. The nucleus of an atom is about
10 000 times smaller. Estimate the radius of the nucleus of a sodium atom.
Write your answer in both nanometres and metres.
● Atomic number and mass number
The number of protons that an atom contains is called its atomic
number. Atoms of different elements have different numbers of
KEY TERM protons. It is the number of protons that determines which element an
Atomic number NNuummbbeerr ooff pprroottoonnss atom is. For example, all atoms with 6 protons are carbon atoms, while
in an atom. all atoms with 7 protons are nitrogen atoms.
4
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Structure of atoms
All atoms are neutral, which means they have no overall electric charge.
TIP
This is because the number of protons (which are positively charged) is
AA ccaarrbboonn aattoomm iiss nneeuuttrraall bbeeccaauussee iitt
the same as the number of electrons (which are negatively charged).
contains 6 protons (charge + 6) and
6 electrons (charge − 6) and so has
Most of the mass of an atom is due to the protons and neutrons.
no overall charge.
Protons and neutrons have the same mass as each other. The mass
number of an atom is the sum of the number of protons and neutrons
KEY TERM
in an atom. For example, an atom of sodium has 11 protons and
Mass number NNuummbbeerr ooff pprroottoonnss ++ 12 neutrons and so has a mass number of 23.
number of neutrons in an atom.
ATOMIC NUMBER = number of protons
MASS NUMBER = number of protons + number of neutrons
The atomic number and mass number of an atom can be used to work
out the number of protons, neutrons and electrons in an atom:
● number of protons = atomic number
● number of neutrons = mass number – atomic number
● number of electrons = atomic number (only for atoms, not ions).
The mass number and atomic number of atoms can be shown as in
Figure 1.2.
Atoms are often shown in the form 23Na. As the atom is a sodium atom,
it must have an atomic number of 11 and so it is not necessary to
23
mass number =
include the atomic number.
N
a
Example
How many protons, neutrons and electrons are there in an atom of 81Br?
11
atomic number = Answer
Number of protons: As the atom is a bromine atom, we can see from looking
mass number: protons + neutrons at the periodic table that the atomic number is 35 and so the atom must have
atomic number: protons 35 protons.
number of protons = 11
number of neutrons = 23 – 11 = 12 Number of neutrons: 81 − 35 = 46 (the mass number minus the number of
number of electrons = 11 protons).
▲ Figure 1.2 Number of electrons: 35 (the same as the number of protons).
● Isotopes
For most elements there are atoms with different numbers of neutrons.
KEY TERM Atoms with the same number of protons but a different number of
Isotopes Atoms with the same neutrons are called isotopes. This means that isotopes have the same
number of protons but a different atomic number but a different mass number.
number of neutrons.
For example, carbon has three isotopes and so there are three different
types of carbon atoms. These are shown in the table below. These three
isotopes are all carbon atoms because they all contain 6 protons, but
they each have a different number of neutrons.
Atom 12C 13C 14C
Protons 6 6 6
Neutrons 6 7 8
Electrons 6 6 6
5
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e Isotopes have a different mass, but their chemical properties are the
bl
same because they contain the same number of electrons.
a
t

c
di Test yourself
o
ri
e
5 List the three particles found inside atoms.
p
e 6 Identify the particle found inside the nucleus of atoms that has no charge.
h
t 7 Atoms contain positive and negative particles. Explain why atoms are

d neutral.
n
a 8 How many protons, neutrons and electrons are there in an atom of 31P?

e
r 9 What is it about the atom 39K that makes it an atom of potassium?
u
t 10 Describe the similarities and differences between atoms of the isotopes
c
u 35Cl and 37Cl.
r
t
s

c
mi Show you can...
o
t
A
Copy and complete the table for each of the elements listed.

1
Element Atomic Mass Number of Number of Number of
number number protons electrons neutrons
7Li
27Al
24Mg
39K
107Ag
● Electron arrangement
The electrons in an atom are in energy levels, also known as shells.
Electrons occupy the lowest available energy levels. The lowest energy level
(the first shell) is the one closest to the nucleus and can hold up to two
electrons. Up to eight electrons occupy the second energy level (the second
shell) with the next eight electrons occupying the third energy level (third
shell). The next two electrons occupy the fourth energy level (fourth shell).
The arrangement of electrons in some atoms are shown in the table. The
electronic structure can be drawn on a diagram or written using numbers.
For example, the electron structure of aluminium is 2,8,3 which means
that it has two electrons in the first energy level, eight electrons in the
second energy level and three electrons in the third energy level.
Atom He F Al K
Atomic number 2 9 13 19
Number of 2 9 13 19
electrons
Electron structure 2 2,7 2,8,3 2,8,8,1
(written)
Electron structure
(drawn)
6
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