Atomic Structure (OCR Gateway 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 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 the Carbon atom

• Atoms are extremely small with a radius of about 1 x 10^-10 metres
  
• The central nucleus contains protons and neutrons only which are packed close together in a small region of space
  
• The radius of the nucleus is about 10 000 times smaller than that of the atom, so it is an extremely small region of space compared to the overall size of the atom
• This means that rather than being evenly spread out throughout the atom, virtually all of the atom's mass is concentrated inside the nucleus
• Electrons have a much smaller mass than protons and neutrons (1 proton has the same mass of around 1840 electrons) and move in the space outside the nucleus in orbits

• Elements are made of tiny particles of matter called atoms
• Each atom is made of subatomic particles called protons, neutrons and electrons
• 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 1836 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:

Relative Mass & Charge of Subatomic Particles Table