CIE AS Chemistry (9701) exams from 2022

Revision Notes

1.1.1 Particles in the Atom & Atomic Structure

Structure of an Atom

  • All matter is composed of atoms which are the smallest parts of an element that can take place in chemical reactions
  • Atoms are mostly made up of empty space surrounding a very small, dense nucleus that contains protons and neutrons
  • The nucleus has an overall positive charge due to the presence of these protons
  • Negatively charged electrons are found in shells in the empty space around the nucleus

Carbon atom structure, IGCSE & GCSE, AS & A Level Chemistry revision notes

The basic structure of an atom (not to scale)

Subatomic Particles

  • Subatomic particles are the particles an element is made up of and include protons, neutrons and electrons
  • These subatomic particles are so small that it is not possible to measure their masses and charges using conventional units (such as grams and coulombs)
  • Instead, their masses and charges are compared to each other using ‘relative atomic masses’ and ‘relative atomic charges
  • These are not actual charges and masses but they are 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 whereas electrons are 1836 times smaller than a proton and neutron
    • Protons are positively charged, electrons negatively charged and neutrons are neutral
  • The relative mass and charge of the subatomic particles are:

Relative mass & charge of subatomic particles table

Atomic Structure Table_Subatomic Particles, downloadable AS & A Level Chemistry revision notes

Exam Tip

The relative mass of an electron is almost negligible.

The charge of a single electron is -1.602 x 10-19  coulombs whereas the charge of a proton is -1.602 x 10-19  coulombs, however, relative to each other, their charges are -1 and +1 respectively.

Atoms: Key Terms

  • The atomic number (or proton number) is the number of protons in the nucleus of an atom and has symbol Z
    • The atomic number is equal to the number of electrons present in a neutral atom of an element
    • Eg. the atomic number of lithium is 3 which suggests that the neutral lithium atom has 3 protons and 3 electrons
  • The mass number (or nucleon number) is the total number of protons and neutrons in the nucleus of an atom and has symbol A
  • The number of neutrons can be calculated by:

Number of neutrons = mass number – atomic number

    • Protons and neutrons are also called nucleons

Exam Tip

Atomic structure notation, IGCSE & GCSE AS & A Level Chemistry revision notes

 The mass (nucleon) and atomic (proton) number are given for each element in the Periodic Table

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.

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