Elements (AQA GCSE Chemistry): Revision Note
Exam code: 8462
Atoms: The building blocks of matter
All substances are made of tiny particles of matter called atoms which are the building blocks of all matter
Each atom is made of subatomic particles called protons, neutrons, and electrons
The protons and neutrons are located at the centre of the atom, which is called the nucleus
The electrons move very fast around the nucleus in orbital paths called shells
The mass of the electron is negligible, hence the mass of an atom is contained within the nucleus where the protons and neutrons are located
The structure of a carbon atom
The atom contains protons, neutrons and electrons
Examiner Tips and Tricks
The atom is the smallest part of an element that exists even though it can be divided into smaller particles.
This is because the atom is the smallest part of an element that still retains the properties of the element - the subatomic particles do not.
Chemical symbols
An element is a pure substance that consists of only one type of atom
It is distinguished by its unique number of protons
Each element is represented by a unique chemical symbol, as shown on the Periodic Table
The most recent Periodic Tables commonly contain around 103 elements although some go up to 118 elements
The chemical symbol for carbon
Rules for writing chemical symbols
A chemical symbol consists of one or two letters.
If the symbol is a single letter, it must be an uppercase letter
For example:
C for carbon
O for oxygen
If the symbol has two letters, the first is always uppercase, and the second is always lowercase
For example:
Na for sodium, not NA
Mg for magnesium, not MG
Atomic & mass numbers
Chemical symbols are often shown with two numbers to provide more detail about the atomic structure
The atomic number (Z) is the number of protons in the nucleus of an atom
It is always the smaller number
It is unique to each element
The mass number (A) is the total number of protons and neutrons in the nucleus
It is always the larger number
Examiner Tips and Tricks
Diatomic elements
Be aware that some non-metal elements exist naturally as molecules containing two atoms (diatomic)
When writing these elements in chemical equations, you must use their molecular formula:
H2, N2, O2, F2, Cl2, Br2, I2
Forgetting to use the '2' for these seven elements is a very common way to lose marks when balancing equations.
The Periodic Table
The Periodic Table of elements
You will be provided with a Periodic Table in your chemistry exams
You need to be able to use the names and symbols for the first 20 elements in the table
You also need to be able to use the name and symbols of the elements in Group 1, Group 7 and any other elements specified in these notes
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