Elements (AQA GCSE Chemistry)

• 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

Chemical symbols

• An element is a substance made of atoms that all contain the same number of protons and cannot be split into anything simpler.
• So, if you had 500g of pure carbon and divided it into 500 x 1g piles, each pile would contain the same substance and would not differ from any other pile.
• There is a limited number of elements, and all elements are found on the Periodic Table e.g., hydrogen, carbon, nitrogen.
  • The most recent Periodic Tables commonly contain around 103 elements although some go up to 118 elements
• Each element is represented by its own unique symbol as seen on the Periodic Table e.g., N stands for nitrogen and for nitrogen only.
• Where a symbol contains two letters, the first one is always written in uppercase letters and the other in lowercase e.g., sodium is Na, not NA.
• The following elements must be written as molecules as they exist in nature as two atoms joined together: H₂, N₂, O₂, F₂, Cl₂, Br₂ and I₂.
• The atomic number and mass number also shown on the periodic table

The symbol key for carbon

C is the symbol for carbon and 12 is the mass number and 6 is the atomic number

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