1. ATOMIC THEORY

2. OBJECTIVES By the end of the lesson you should be able to:
Describe how the atomic theory was developed and who was involved in the process

3. HISTORICAL UNDERSTANDING
Chinese: world was based on 5 elements (earth, water, fire, metal and wood)
Balance

4. HISTORICAL UNDERSTANDING
Greeks: Democritus argued that matter could be endlessly divided until reaching the atomos (smallest piece)
We use the word atom today from this origin
Atoms cannot be divided any further or destroyed
Matter is made of tiny particles that exist in empty space

5. HISTORICAL UNDERSTANDING
Aristotle did not agree; he believed
Earth, air, fire, and water!
Nobody challenged the idea again for 2000 years!

6. Alchemists in the Middle Ages tried to turn common metals into gold - nobody succeeded!
They tried for 1000 years!

7. ATOMIC THEORY DEVELOPMENT
The Revolution!
John Dalton, J.J. Thomson, Ernest Rutherford and Niels Bohr all played a very important part in the development of the atomic theory

8. JOHN DALTON (1766 – 1844) Dalton’s Atomic Theory:
All matter is made up of small particles called atoms
Atoms cannot be created, destroyed or divided into smaller particles
All atoms of the same element are identical in mass and size but they are different in mass and size from atoms of other elements
Compounds are created when atoms of different elements link together in definite proportions

9. JOHN DALTON (1766 – 1844)

10. J.J. THOMSON (1856 – 1940)
Used electric currents in gas discharge tubes to determine that currents were negative charges
Found all substances could produce these currents so all substances had negative charges
Atoms therefore had smaller negative charges which he called electrons

11. J.J. THOMSON (1856 – 1940)
Proposed the “Raisin Bun Model” which was a positively charged bun with negatively charged raisins in it

12. ERNEST RUTHERFORD (1871 – 1937) Student of J.J. Thomson
Shot positive (alpha) particles at a piece of gold foil and saw that some bounced off while most went straight through
Discovered nucleus of an atom (dense positively charged centre of an atom)
Nucleus is made of positive charges and neutral charges

13. Rutherford Video Explained

14. NIELS BOHR (1885 – 1962)
Worked under Rutherford and knew that around the nucleus were negative charges
Found that gases would glow if an electric current passes through them (i.e. Neon signs)
Negative charges have certain amount of energy and are in “orbit” around the nucleus like planets around the sun.

16. A REVOLUTION

17. HISTORY of the ATOM TIMELINE
Antoine Lavoisier
makes a substantial number of contributions to the field of Chemistry
J.J. Thomson discovers the electron and proposes the Plum Pudding Model in 1897
Niels Bohr proposes the Bohr Model in 1913
James Chadwick discovered the neutron in in 1932
1766 – 1844
1871 – 1937
1887 – 1961
460 – 370 BC
1700s
1800s
1900s
Erwin Schrodinger describes the electron cloud in 1926
Democritus proposes
the 1st atomic theory
John Dalton proposes his atomic theory in 1803
Ernest Rutherford performs the Gold Foil Experiment in 1909
1891 – 1974
1743 – 1794
1885 – 1962
1856 – 1940
Click on picture for more information

18. PROGRESSION of the ATOMIC MODEL Democritus & John Dalton+ -
The structure of an atom, according to:
Democritus & John Dalton
James Chadwick
J.J. Thomson
Neils Bohr
Ernest Rutherford
Erwin Schrodinger

21. ATOMIC STRUCTURE

22. A REVOLUTION

23. ATOMIC STRUCTURE Atoms are made up of 3 smaller sub-atomic particles
Protons
Neutrons
Electrons

24. ATOMIC STRUCTURE Energy Shells Nucleus
Protons and neutrons are found in the nucleus of the atom
Electrons are found around the nucleus in “energy shells” or “orbitals”
Energy Shells
Nucleus

25. SUB-ATOMIC PARTICLES Name Symbol Relative Mass Electric Charge
Location in Atom
Proton p+ 1 +
Nucleus
Neutron no
Electron e-
1/1837 -
Shells

26. Draw an atom! Include the 3 sub-atomic particles in the correct locations (part of nucleus, around nucleus) and their charge (positive, neutral, negative)
Be sure to clearly label your drawing!