Atomic Structure (WJEC GCSE Chemistry: Combined Science)

• 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 nucleus is positively charged 
• 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

Atomic Structure Diagram 

 The structure of the carbon atom

• The protons, neutrons and electrons that an atom is made up of are called subatomic particles
• These subatomic particles are so small that it is not practical to measure their masses and charges using conventional units (such as grams or coulombs)
• Instead, their masses and charges are compared to each other, and so are called ‘relative atomic masses’ and ‘relative atomic charges’
• These are not actual charges and masses, but rather charges and masses of particles relative to each other
  • Protons and neutrons have a very similar mass, so each is assigned a relative mass of 1
  • Electrons are 2000 times smaller than a proton and neutron, and so their mass is often described as being negligible

• The relative mass and charge of the subatomic particles are:

The Mass & Charge of Subatomic Particles Table

Particle	Relative Mass	Charge
Proton	1	+1
Neutron	1	0 (neutral)
Electron	1/2000	-1

• Atoms are electrically neutral
• This is achieved by having the same number of electrons as protons
• The negative charge of an electron exactly cancels out the positive charge of a proton
• An ion is formed when an atom loses or gains electrons to achieve a full outer shell 
  • If an atom loses electrons, it forms positively charged ions 
  • If an atom gains electrons, it forms negatively charged ions