Fundamental Particles (Oxford AQA International A Level Chemistry) : Revision Note

The Structure of an Atom

• All matter is composed of atoms

• Atoms are the smallest parts of an element that can take place in chemical reactions

• Atoms are mostly made up of empty space around a very small, dense nucleus that contains protons and neutrons

• Protons and neutrons are sometimes referred to as nucleons because they are found in the nucleus

• The nucleus has an overall positive charge

  • This is because the protons have a positive charge and the neutrons have a neutral charge

• Negatively charged electrons are found in orbitals in the empty space around the nucleus

• Our understanding of the atomic model has evolved over time as a result of evidence from various investigations and experiments

The structure of an atom

Subatomic Particles

• Protons, neutrons and electrons are so small that it is not practical to measure their charges using conventional units, such as coulombs

• Instead, their charges are compared to each other

  • This is why they are called relative electrical charges

• The relative electrical charges and masses of the subatomic particles are:

Table of relative electrical charges

• Atoms have no overall charge

• This is because they have the same number of positive protons as negative electrons

  • The negative charge of one electron exactly cancels out the positive charge of one proton

• Ions are formed when an atom loses or gains electrons to achieve a full outer shell 

  • If an atom loses one negative electron, it forms a positively charged 1+ ion 

  • If an atom gains one negative electron, it forms a negatively charged 1- ion