1. Discovery of the Atom

2. Democritus Born in Abdera about 460 B.C.
Proposed that all matter is composed of atoms

3. Antoine Lavoisier (1743-1794) Established the Law of
Conservation of Mass which stated
that matter could neither be created or destroyed

4. John Dalton (1776-1844) British chemist and physicist
who developed the atomic
theory of matter.

5. Dalton’s Atomic Theory
Elements are composed of particles called atoms.
Atoms of a given element are identical, but differ from those of any other element.
Atoms are neither created or destroyed.
A given compound always has the same relative numbers and kinds of atoms.

6. Niels Bohr (1885-1962) Proposed a planetary model
of the atom saying that
electrons exist in distinct orbits.

7. The Bohr Atom

8. J.J. Thomson (1856-1940) Used cathode ray tubes to discover
the electron.

9. Robert A. Millikan (1868-1953) His earliest major success
was the determination of the
charge and mass of a single
electron.

11. Ernest Rutherford ( )
Determined that all of an atom’s positive
charge as well as most of it’s mass was
concentrated in a small core which he
called the nucleus. .

13. Rutherford’s Model

14. Modern Atomic Theory
The Quantum Atom