1. 1.3 – 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
Draw and describe an atom using 4 major properties

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

4. HISTORICAL UNDERSTANDING
Greeks: argued that matter could be endlessly divided until reaching the atomos (smallest piece)
We use the word atom today from this origin

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

15. A REVOLUTION

16. ATOMIC STRUCTURE
Atom: smallest part of an element that keeps the properties of the element
Is made up of 3 smaller sub-atomic particles
Protons
Neutrons
Electrons

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

18. 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!