The discovery of the electron

Atomic Structure Concepts

  • Matter consists of tiny, indivisible particles called atoms.

  • Atoms are made of subatomic particles: electrons, protons, and neutrons.

Cathode Ray Experiments

  • Conducted by J.J. Thomson to discover electrons.

  • JJ Thompson discovered the charge to mass ratio of the electron.

  • Cathode rays consist of negatively charged particles (electrons).

  • JJ thompson discovered that the electron was a low mass particle.

  • The charged pushed away from the negative and towards the positive. Showing that electrons are negatively charged because opposites attract.

  • Observations:

    • Cathode rays bend towards positive plates, indicating negative charges.

    • All metals emit cathode rays when used as cathodes, suggesting all metals contain electrons.

Key Discoveries

  • Millikan's Oil Drop Experiment:

  • Identifying the electron is negatively charged. Determined the EXACT charge and mass of the electron.

    • Charge of an electron: -1.60 \times 10^{-19} C.

    • Mass of an electron: 9.11 \times 10^{-31} kg.

Atomic Model

  • Thomson proposed the "Plum Pudding Model" (positive and negative charge distributed in the atom).

Zepto (zC) prefix multiplier is 10^-21

J.J. Thompson DID NOT contribute to determining the exsct charge pf the electron.