1. The Atomic Theory

2. Atom  The smallest particle into which an element can be divided and still be the same substance.  The smallest particle of an element that retains the properties of that element.

3. The Atom

4. Protons and Neutrons

5. Atomic Theory  The existence of atoms is not a new idea.  Atomic theory has been around for more than 2,000 years.  A theory is a unifying explanation for a broad range of hypotheses and observations that have been supported by testing.

6. John Dalton  All substances are made of atoms.  Atoms are small particles that cannot be created, divided, or destroyed.  Atoms of the same element are exactly alike, and atoms of different elements are different.  Atoms join with other atoms to make new substances.

9. J.J. Thomson  Thomson discovered that there are small particles inside the atom.  Therefore, atoms can be divided into even smaller parts.  Thomson’s model became known as “Plum Pudding”  JJ Thomson is credited with discovering “ELECTRONS”

12. Ernest Rutherford  Rutherford proposed that in the center of the atom is a tiny, extremely dense, positively charged region called the “NUCLEUS”.

15. Rutherford’s Model

16. James Chadwick  The Neutron, one of the particles in the “Nucleus” of an Atom, is discovered by British physicist James Chadwick.

17. Niels Bohr  Bohr suggested that electrons traveled around the nucleus in definite paths.  Bohr proposed the “Planetary “ path version.  He proposed that no paths are located between the levels, but electrons can jump from a path in one level to a path in another level.  A very good example of this would be a “ladder”.

20. Bohr’s Model

21. The Modern Theory  According to the current theory, electrons do not travel in definite paths as Bohr suggested.  In fact their paths can not be predicted.  Regions inside the atom where electrons are likely to be found are called “ELECTRON CLOUDS”.

22. The Modern Theory