Historical Development of the Atom
Explain the contributions made by each of the following in the development of our
understanding of the atom.
1. Democritus: first one to state that atoms existed.
2. John Dalton: developed the atomic theory; had a solid sphere as his model—like a
billiard ball.
3. J. J. Thomson: discovered the electron; had the plum pudding model—but What does
that mean-*think chocolate chip ice cream
4. Ernest Rutherford: performed the gold foil experiment; determined atoms are mostly
empty space, have a nucleus which is positively charged and massive
5. Robert Millikan: determined the charge and mass of an electron
6. Neils Bohr: electrons move in orbits around the nucleus—called the Planetary model;
stated electrons in atoms have fixed amounts of energy
7. Dmitri Mendeleev: first one to arrange periodic table—done in columns by increasing
atomic mass
8. Henry Moseley: arranged periodic table by increasing atomic number
9 Max Planck energy atoms can only change in small fixed amounts known as quanta
10. Werner Heisenberg: developed uncertainty principle- you can know where an
electron is or its speed but not both.
11. Louis de Broglie: developed the Quantum mechanical model.