Atomic Structure (Edexcel GCSE Chemistry: Combined Science)

Revision Note

Test yourself
Stewart

Author

Stewart

Last updated

Did this video help you?

The Structure of an Atom

  • Elements are made of tiny particles of matter called atoms
  • Each atom is made of subatomic particles called protons, neutrons and electrons
  • Their size is so tiny that we can't really compare their masses in conventional units such as kilograms or grams, so a unit called the relative atomic mass is used
  • The mass of an atom is concentrated in the nucleus, because the nucleus contains the heaviest subatomic particles (the neutrons and protons)
  • The nucleus is also positively charged due to the protons
  • Electrons orbit the nucleus of the atom, contributing very little to its overall mass, but creating a ‘cloud’ of negative charge
  • The electrostatic attraction between the positive nucleus and negatively charged electrons orbiting around it is what holds an atom together

Atomic Structure Mass and Charge Distribution, downloadable AS & A Level Chemistry revision notes

The mass of the atom is concentrated in the positively charged nucleus which is attracted to the negatively charged electrons orbiting around it

The Sub-atomic Particles

  • The protonsneutrons 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 1840 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

Atomic Structure & the Periodic Table table, IGCSE & GCSE Chemistry revision notes

  • 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

Examiner Tip

The mass of an electron can just be stated as 'negligible' or 'very small' in an exam. You do not need to learn the value.

You've read 0 of your 10 free revision notes

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Stewart

Author: Stewart

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Exam Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.