CIE AS Chemistry (9701) exams from 2022

Revision Notes

1.1.2 Mass, Charge & Subatomic Particles

Mass & Charge Distribution

  • The mass of an atom is concentrated in the nucleus as the nucleus contains the heaviest subatomic particles (the neutrons and protons)
    • The mass of the electron is negligible
  • 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 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

Behaviour of Subatomic Particles in an Electric Field

  • Protons, neutrons and electrons behave differently when they move at the same velocity in an electric field
  • When a beam of electrons is fired past the electrically charged plates, the electrons are deflected very easily away from the negative plate towards the positive plate
    • This suggests that the electron is negatively charged as like charges repel each other
    • It also shows that electrons have a very small mass as they are easily deflected
  • A beam of protons is deflected away from the positive plate towards the negative plate
    • This suggests that the proton is positively charged
    • As protons are deflected less than electrons, this shows that protons are heavier than electrons
  • A beam of neutrons is not deflected at all
    • Which suggests that the particle is neutral in character as it is not attracted to either the negative or positive plate

Atomic Structure Behaviour of Particles in an Electric Field, downloadable AS & A Level Chemistry revision notes

The lighter electrons undergo much more deflection than the protons

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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