1. Discovery of the Atom

2. Democritus  Democritus was an ancient Greek who had a philosophical idea of an atom.  His approach was not based on the scientific method.

3. Dalton  Dalton transformed the philosophical concept of an atom into a scientific theory.  A.)  All elements are composed of indivisible atoms.  What does indivisible mean?  Cannot be divided.  B.)  Atoms of the same element are identical.  Atoms of different elements are different.  C.)  Atoms combine in fixed ratios to form compounds.  D.)  Chemical reactions occur when atoms are rearranged.

4. What does subatomic mean?  Smaller than atomic

5. What are the three kinds of subatomic particles?  Protons, Neutrons and Electrons

6. Who discovered the electron?  J.J. Thomson

7. What did the cathode-ray tube experiment allow to be concluded?  Electrons are in ALL atoms.

8. Millikan  Millikan found the quantity of charge carried by an electron.  This allowed the calculation of the mass of the electron. It’s mass is 1/1840 the mass of a hydrogen atom.

9. Atoms are electrically neutral.  Positively charged subatomic particles are called protons.  Subatomic particles with no charge are called neutrons.

10. Rutherford  Rutherford’s gold-foil experiment gave evidence of the atomic nucleus.  Alpha particles were aimed at a sheet of gold foil.

11. Rutherford’s Gold Foil Experiment  Most of the particles passed through.  A few of the particles bounced back.  It was concluded that an atom is mostly empty space.  The mass and positive charge are concentrated in the nucleus.

12. Atom Make-Up  The protons and neutrons are located in the nucleus.  The electrons are distributed around the nucleus and occupy  almost all of the volume of the atom.