• STM (scanning tunnelling microscope)

  • pass a fine charged needle over the surface of an object

  • Current changes depending on hte distance betweent the surface and needle

  • Showing little “bumps” of atoms

  • Allows us to see individual atoms

• John Dalton

  • first modern atomic theory

  • elements consist of atoms, which cannot be created, destroyed, or divided, and atoms of the same element have identical size, mass, and other properties

J.J Thompson and his cathode ray tube

• proving existence of electrons

• applying high voltage to a tube with a metal electrode at the end

  • A ray was produced from the negative electrode

  • Can produce a visible ray

  • Ray are electrons

• Blueberry muffin model 🔵🧁

  • Electrons are negatively charged blueberries

  • Positively charged muffin

• Atoms had to contain electrons

  • electrons in a cloud of positive charge

Radioactivity

• Radioactivity is the spontaneous decay of the nucleus of an atom

• Emitting alpha particles

• Proposed by Ernest Rutherford

• Earlier contribution was Henri Becquerel

  • without light, a piece of material with uranium produced an image on a photographic plate

    • spontaneously emitting radiation

Gold Foil Experiment

• Put a radioactive substance into a lead box with a small hole in it

• The hole would be where the alpha particles escape from

• The particles would shoot out and hit gold foil

• Thought all particles would go right through

  • Most would go through but some deflected or repelled off

  • The dense centre or nucleus would have deflected while the outside (electrons) that had a low density would have passed through

• Findings:

  • An atom has a dense, + charged centre

  • An atom is mostly empty

  • The centre of the atom is positively charged, repelling the positively charged alpha particles