1. Introduction to the Atomic Theory

2. What is the Atomic Theory? – The Atomic theory is the study of the nature of atoms and how they combine to form all types of matter. – There have been a number of theories that have been proposed to explain how atoms work. Significant contributors are: Democritus 440 BCE, John Dalton (1766 – 1844), J. J. Thomson (1856 – 1940), Earnest Rutherford (1891 – 1937), James Chadwick (1891 – 1974), and Niels Bohr (1885 – 1962). (See p176 for a more detailed look at significant historical figures)

3. Dalton’s Atomic Theory All matter is made of small, dense, indestructible particles called atoms. The atoms of an element are identical to one another. The atoms of different elements have different properties (mass and size). Atoms can join together to form groups of atoms called molecules. (can form new substances)

4. Electrons and Protons discovered by J.J. Thomson J.J. Thomson used a cathode ray to discover there were negatively charged particles found in atoms. These negatively charged particles would be called electrons. He then reasoned that if the atoms contained negatively charged particles there must be positively charged particles since atoms themselves do no contain a charge.

5. J.J. Thomson’s Model Source) http://www.kutl.kyushu-u.ac.jp/seminar/MicroWorld1_E/Part2_E/P24_E/Thomson_model_E.htm

6. Video example of Cathode Ray http://youtu.be/O9Goyscbazk Click on the above link to watch a video demonstrating how a cathode ray works.

7. Earnest Rutherford discovers the nucleus Ernest Rutherford discovered the nucleus and realized it is very very small compared to the rest of the atom. Source: http://www.iun.edu/~cpanhd/C101webnotes/modern-atomic-theory/rutherford-model.html

8. Ernest Rutherford Video http://youtu.be/5pZj0u_XMbc Click on the above link to watch a video explaining Ernest Rutherford’s experiment

9. Chadwick’s discovery of the neutrons http://youtu.be/HnmEI94URK8 Click on the above link to watch a video explaining Chadwick’s discovery of the neutron.

10. Bohr arranges the electrons outside the nucleus Bohn believed that electrons surrounded the nucleus in specific energy levels. Each shell contained only a specific number of electrons with the maximum number of electrons that can exist in the first shell is 2, second shell 8 and third shell 8.

11. Examples of a Bohr Diagram http://www.online.bcelearner.ca/login/index.php

12. Quantum Mechanical Model This is the model physicists and chemists use today. Electrons exists in different energy levels and surround the nucleus in a form resembling a cloud.

13. Example of a Quantum Mechanical Model of an Atom http://pdgusers.lbl.gov/~pslii/uabackup/fundamentals/matter/1300200.html

14. What is an atom? – An atom is the smallest part of an element that has all of the element’s properties. – It contains the following subatomic particles: electrons (negatively charged), protons (positively charged), and neutrons (no charge). – Electrons are the smallest part of an atom, having the relative mass of 1, while protons have the relative mass of 1836, and neutrons have the relative mass of 1837. – Protons and neutrons are contained in the nucleus while electrons surround the nucleus in different energy levels.