GCSE SCIENCE REVISION NOTES
Edexcel GCSE Chemistry
Complete revision notes · Higher tier · Specification 1CH0
All 9 topics, Papers 1 and 2 All 8 core practicals Worked examples
Quick-check questions with answers Contents page and numbered pages
Pastel colour-coded by topic · Written to follow the Pearson Edexcel GCSE (9-1) Chemistry specification
Independent notes, not produced or endorsed by Pearson or Edexcel
,Contents
1 Key concepts in chemistry 3
2 States of matter and mixtures 9
3 Chemical changes 12
4 Extracting metals and equilibria 17
5 Separate chemistry 1 20
6 Groups in the periodic table 24
7 Rates of reaction and energy changes 27
8 Fuels and Earth science 30
9 Separate chemistry 2 33
Core practical reference sheet 39
Exam checklist 40
How to use these notes
Each topic starts with a coloured banner. The same colour is used for that topic throughout, so you can
find it fast.
Key points are the facts the exam expects. Definitions (orange boxes) are worth learning word for
word.
Worked examples (blue boxes) show every step of the calculations. About 20% of the chemistry marks
are for maths skills, so practise these until they are automatic.
Core practicals (green boxes) are the 8 required practicals. You will be asked about their methods in the
exam.
Quick checks (purple boxes) end every topic. Cover the answers, try the questions, then mark yourself.
Amber boxes are higher tier only content. Everything in this pack can be examined on the higher
papers.
Exam tips (pink boxes) flag the mistakes examiners see most.
Your exam at a glance
Paper 1 (1CH0/1H) Paper 2 (1CH0/2H)
Topics 1, 2, 3, 4, 5 1, 6, 7, 8, 9
Time 1 hour 45 minutes 1 hour 45 minutes
Marks 100 100
Question styles Multiple choice, short answer, calculations and extended open-response questions
Higher tier targets grades 4 to 9, with a safety-net grade 3. The hardest questions on each paper only
appear on the higher tier, so learn the amber higher-tier-only boxes as carefully as the shared content.
Calculators are allowed, and you get a periodic table in the exam.
Edexcel GCSE Chemistry · Higher · page 2 of 40
, TOPIC 1 · PAPERS 1 AND 2
Key concepts in chemistry
1.1 Atomic structure
The model of the atom has changed over time as new evidence was found. Dalton pictured atoms as solid
spheres. Thomson discovered the electron, leading to the "plum pudding" model. Rutherford showed the
atom is mostly empty space with a tiny, positive, dense nucleus. Bohr placed electrons in fixed shells, and
Chadwick discovered the neutron.
An atom has a tiny central nucleus containing protons and neutrons, surrounded by electrons in
shells. The nucleus is very small compared with the overall size of the atom, but almost all of the atom's
mass is concentrated in it.
Particle Relative mass Relative charge
Proton 1 +1
Neutron 1 0
Electron 1/1840 (almost 0) −1
Atoms have equal numbers of protons and electrons, so the positive and negative charges cancel
and atoms are neutral overall.
DEFINITIONS
Atomic number: the number of protons in the nucleus (unique to each element). Mass number: the
total number of protons plus neutrons in the nucleus.
1.2 Isotopes and relative atomic mass
DEFINITION
Isotopes: different atoms of the same element with the same number of protons but different
numbers of neutrons.
WORKED EXAMPLE · PROTONS, NEUTRONS, ELECTRONS
An atom of sodium has atomic number 11 and mass number 23. How many protons, neutrons and
electrons does it have?
Protons = atomic number = 11. Atoms are neutral, so electrons = 11. Neutrons = mass number − atomic
number = 23 − 11 = 12.
Isotopes explain why some relative atomic masses are not whole numbers: the relative atomic mass (Ar) is
a weighted mean of the masses of an element's isotopes, taking their abundances into account. Chlorine,
for example, is a mixture of chlorine-35 and chlorine-37, giving Ar = 35.5.
Edexcel GCSE Chemistry · Higher · page 3 of 40
, HIGHER TIER ONLY Calculating relative atomic mass (1.12): Ar is the weighted mean of the
isotope masses. Multiply each isotope mass by its abundance, add the results, and divide by the total
abundance. Example: chlorine is 75% chlorine-35 and 25% chlorine-37, so Ar = (35 × 75 + 37 × 25) ÷ 100
= 2625 + 925 = 3550 ÷ 100 = 35.5. You can be given abundances as percentages, ratios or spectra peaks.
1.3 The periodic table
Mendeleev arranged the known elements in order of relative atomic mass and grouped them by the
properties of the elements and their compounds. He left gaps and used his table to predict the existence
and properties of undiscovered elements; when those elements were later found, their properties
matched his predictions. He thought he had arranged elements strictly by relative atomic mass, but this
was not always true (some pairs had to be swapped) because of the relative abundance of isotopes. In the
modern table, elements are arranged in order of increasing atomic number, which fixes those anomalies.
In the modern periodic table, elements are arranged in order of increasing atomic number, in rows
called periods. Elements with similar properties sit in the same vertical column (group); elements
in the same group have the same number of electrons in their outer shell.
HIGHER TIER ONLY Electron configuration and position (1.20): the electronic configuration tells
you exactly where an element sits: the group number equals the number of electrons in the outer
shell, and the period number equals the number of occupied shells. So an element with
configuration 2,8,6 is in group 6, period 3. This explains why group members react alike: reactions
involve only the outer electrons, which are arranged the same way down the group.
Metals are found on the left and in the middle of the table; non-metals on the right. This division links to
atomic structure: metal atoms have few outer-shell electrons and tend to lose them to form positive ions,
while non-metal atoms tend to gain or share electrons.
WORKED EXAMPLE · ELECTRON ARRANGEMENTS
Write the electron arrangement of (a) chlorine, atomic number 17, and (b) calcium, atomic number 20.
Fill the shells in order (first shell holds 2, then up to 8): (a) chlorine = 2,8,7; (b) calcium = 2,8,8,2. You
need to be able to do this for the first 20 elements, as numbers and as shell diagrams.
1.4 Ionic bonding
DEFINITION
Ion: an atom or group of atoms with a positive or negative charge.
An ionic bond forms when electrons are transferred from a metal atom to a non-metal atom. The metal
loses electrons to become a positive ion (cation); the non-metal gains electrons to become a negative ion
(anion). The strong electrostatic attraction between the oppositely charged ions is the ionic bond. Show this
with dot and cross diagrams, e.g. Na (2,8,1) transfers one electron to Cl (2,8,7) to give Na+ (2,8) and Cl−
(2,8,8).
Ions in ionic compounds form so that each ion gets a full outer shell. This topic limits you to
compounds of groups 1, 2, 6 and 7: group 1 metals form 1+ ions, group 2 form 2+, group 6 non-metals
form 2−, group 7 form 1−.
Edexcel GCSE Chemistry · Higher · page 4 of 40
Edexcel GCSE Chemistry
Complete revision notes · Higher tier · Specification 1CH0
All 9 topics, Papers 1 and 2 All 8 core practicals Worked examples
Quick-check questions with answers Contents page and numbered pages
Pastel colour-coded by topic · Written to follow the Pearson Edexcel GCSE (9-1) Chemistry specification
Independent notes, not produced or endorsed by Pearson or Edexcel
,Contents
1 Key concepts in chemistry 3
2 States of matter and mixtures 9
3 Chemical changes 12
4 Extracting metals and equilibria 17
5 Separate chemistry 1 20
6 Groups in the periodic table 24
7 Rates of reaction and energy changes 27
8 Fuels and Earth science 30
9 Separate chemistry 2 33
Core practical reference sheet 39
Exam checklist 40
How to use these notes
Each topic starts with a coloured banner. The same colour is used for that topic throughout, so you can
find it fast.
Key points are the facts the exam expects. Definitions (orange boxes) are worth learning word for
word.
Worked examples (blue boxes) show every step of the calculations. About 20% of the chemistry marks
are for maths skills, so practise these until they are automatic.
Core practicals (green boxes) are the 8 required practicals. You will be asked about their methods in the
exam.
Quick checks (purple boxes) end every topic. Cover the answers, try the questions, then mark yourself.
Amber boxes are higher tier only content. Everything in this pack can be examined on the higher
papers.
Exam tips (pink boxes) flag the mistakes examiners see most.
Your exam at a glance
Paper 1 (1CH0/1H) Paper 2 (1CH0/2H)
Topics 1, 2, 3, 4, 5 1, 6, 7, 8, 9
Time 1 hour 45 minutes 1 hour 45 minutes
Marks 100 100
Question styles Multiple choice, short answer, calculations and extended open-response questions
Higher tier targets grades 4 to 9, with a safety-net grade 3. The hardest questions on each paper only
appear on the higher tier, so learn the amber higher-tier-only boxes as carefully as the shared content.
Calculators are allowed, and you get a periodic table in the exam.
Edexcel GCSE Chemistry · Higher · page 2 of 40
, TOPIC 1 · PAPERS 1 AND 2
Key concepts in chemistry
1.1 Atomic structure
The model of the atom has changed over time as new evidence was found. Dalton pictured atoms as solid
spheres. Thomson discovered the electron, leading to the "plum pudding" model. Rutherford showed the
atom is mostly empty space with a tiny, positive, dense nucleus. Bohr placed electrons in fixed shells, and
Chadwick discovered the neutron.
An atom has a tiny central nucleus containing protons and neutrons, surrounded by electrons in
shells. The nucleus is very small compared with the overall size of the atom, but almost all of the atom's
mass is concentrated in it.
Particle Relative mass Relative charge
Proton 1 +1
Neutron 1 0
Electron 1/1840 (almost 0) −1
Atoms have equal numbers of protons and electrons, so the positive and negative charges cancel
and atoms are neutral overall.
DEFINITIONS
Atomic number: the number of protons in the nucleus (unique to each element). Mass number: the
total number of protons plus neutrons in the nucleus.
1.2 Isotopes and relative atomic mass
DEFINITION
Isotopes: different atoms of the same element with the same number of protons but different
numbers of neutrons.
WORKED EXAMPLE · PROTONS, NEUTRONS, ELECTRONS
An atom of sodium has atomic number 11 and mass number 23. How many protons, neutrons and
electrons does it have?
Protons = atomic number = 11. Atoms are neutral, so electrons = 11. Neutrons = mass number − atomic
number = 23 − 11 = 12.
Isotopes explain why some relative atomic masses are not whole numbers: the relative atomic mass (Ar) is
a weighted mean of the masses of an element's isotopes, taking their abundances into account. Chlorine,
for example, is a mixture of chlorine-35 and chlorine-37, giving Ar = 35.5.
Edexcel GCSE Chemistry · Higher · page 3 of 40
, HIGHER TIER ONLY Calculating relative atomic mass (1.12): Ar is the weighted mean of the
isotope masses. Multiply each isotope mass by its abundance, add the results, and divide by the total
abundance. Example: chlorine is 75% chlorine-35 and 25% chlorine-37, so Ar = (35 × 75 + 37 × 25) ÷ 100
= 2625 + 925 = 3550 ÷ 100 = 35.5. You can be given abundances as percentages, ratios or spectra peaks.
1.3 The periodic table
Mendeleev arranged the known elements in order of relative atomic mass and grouped them by the
properties of the elements and their compounds. He left gaps and used his table to predict the existence
and properties of undiscovered elements; when those elements were later found, their properties
matched his predictions. He thought he had arranged elements strictly by relative atomic mass, but this
was not always true (some pairs had to be swapped) because of the relative abundance of isotopes. In the
modern table, elements are arranged in order of increasing atomic number, which fixes those anomalies.
In the modern periodic table, elements are arranged in order of increasing atomic number, in rows
called periods. Elements with similar properties sit in the same vertical column (group); elements
in the same group have the same number of electrons in their outer shell.
HIGHER TIER ONLY Electron configuration and position (1.20): the electronic configuration tells
you exactly where an element sits: the group number equals the number of electrons in the outer
shell, and the period number equals the number of occupied shells. So an element with
configuration 2,8,6 is in group 6, period 3. This explains why group members react alike: reactions
involve only the outer electrons, which are arranged the same way down the group.
Metals are found on the left and in the middle of the table; non-metals on the right. This division links to
atomic structure: metal atoms have few outer-shell electrons and tend to lose them to form positive ions,
while non-metal atoms tend to gain or share electrons.
WORKED EXAMPLE · ELECTRON ARRANGEMENTS
Write the electron arrangement of (a) chlorine, atomic number 17, and (b) calcium, atomic number 20.
Fill the shells in order (first shell holds 2, then up to 8): (a) chlorine = 2,8,7; (b) calcium = 2,8,8,2. You
need to be able to do this for the first 20 elements, as numbers and as shell diagrams.
1.4 Ionic bonding
DEFINITION
Ion: an atom or group of atoms with a positive or negative charge.
An ionic bond forms when electrons are transferred from a metal atom to a non-metal atom. The metal
loses electrons to become a positive ion (cation); the non-metal gains electrons to become a negative ion
(anion). The strong electrostatic attraction between the oppositely charged ions is the ionic bond. Show this
with dot and cross diagrams, e.g. Na (2,8,1) transfers one electron to Cl (2,8,7) to give Na+ (2,8) and Cl−
(2,8,8).
Ions in ionic compounds form so that each ion gets a full outer shell. This topic limits you to
compounds of groups 1, 2, 6 and 7: group 1 metals form 1+ ions, group 2 form 2+, group 6 non-metals
form 2−, group 7 form 1−.
Edexcel GCSE Chemistry · Higher · page 4 of 40
