1. Who am I?

2. Democritus
He said you cannot cut a piece of matter infinitely, but at some point you would get the smallest piece of matter possible.
All matter is composed of tiny, indivisible particles called “atomos”.
450 BC
Greek Philosopher

3. John Dalton 1803-School teacher
Studied the ratios in which elements combine in chemical reactions
Formulated first Atomic theory of matter:
Each element is composed of extremely small particles called atoms.
All atoms of a given element are identical, but they differ from those of any other element
Atoms are neither created nor destroyed in any chemical reaction.
A given compound always has the same composition or ratio of each atom

4. JJ Thomson
England 1897
He discovered the electron while experimenting with cathode rays.
He determined that the cathode ray was made of negatively charged particles – electrons.
He also was able to estimate that the mass of the electron was equal to about 1/1800 of the mass of a hydrogen atom.
His discovery of the electron won the Nobel Prize in 1906.
He showed that the production of the cathode ray was not dependent on the type of gas in the tube, or the type of metal used for the electrodes. He concluded that these particles were part of every atom.
He created the “plum pudding model” of the atom.

5. Ernest Rutherford Born in New Zealand 1871-1937
Tested Thomson’s theory of atomic structure with the “gold foil” experiment in 1910.
Bombarded thin gold foil with a beam of ‘alpha’ particles.
If the positive charge was evenly spread out, the beam should have easily passed through.
All of the positive charge and most of the mass of an atom are concentrated in a small core, called the nucleus.
Gold Foil Experiment (alpha scattering)
he determined that an atom’s positive charge and most of its mass was concentrated in the core (most of the atom is empty space)
he named the core “the nucleus”

6. Cathode Ray Tube Experiment
Performed by JJ Thomson
Showed the existence of the electron.
The ray is negative and composed of electrons.
The negative end of a magnet attracts the beam.

7. Gold Foil Experiment Performed by Ernest Rutherford
Positive alpha particles were shot at a thin sheet of gold foil
The deflection of the beam indicated the existence of a small, positively charged nucleus.

8. Thomson’s Model of the Atom
Called the “plum pudding” model
The atom was comprised of positively charged matter with negative electrons “stuck” in the positive “pudding”

9. Rutherford’s Model of the Atom
Contained a positive nucleus
Electrons were around the outside of the nucleus

10. Bohr Model of the Atom Nucleus in center with protons and neutrons
Electrons are orbiting the nucleus in a set pattern
Each orbital has a unique amount of energy

11. Quantum Model of the Atom
Contains a nucleus with protons and neutrons
Electrons move very quickly around the nucleus, not in a circle or orbit, but randomly within an electron cloud.