1. 1-3A Behaviour of Gases Demo
1.3 Atomic Theory
1-3A Behaviour of Gases Demo

2. Early Greek Philosophers (5th century BC)
Debated what the universe was made up of
Democritus theorizes that everything made of tiny particles he calls atomos

3. Aristotle (4th century BC)
Lived 2500 years ago
Most respected Greek philosopher
Creator of the “4 elements” theory
Believed that everything in the world was made up of earth, air, fire & water

4. The Alchemists Aristotles theory persisted for over 2000 years!
During the middle ages, everyone was attempting alchemy.
These attempts were all unsuccesful, but resulted in an enormous amount of accidental scientific discoveries!
These discoveries had many questioning Aristotles 4 elements theory

5. John Dalton (1766 – 1844)
Credited with disproving Aristotle and developing a new way of explaining matter
Video of Dalton’s candle/water/jar experiment
Since the flame ‘used up’ something in the air, obviously air could be broken down further, so was not a building block of matter!

6. Dalton’s Atomic Theory
All matter is made 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 the atoms of other elements.
Compounds are created when atoms of different elements link together in definite proportions.

7. Dalton’s theory shows why the alchemists were never successful.
Metals are made of specific atoms, and atoms cannot be turned into other atoms!!

8. J.J. Thomson (1856-1940) British physicist
Studied electric currents in gas discharge tubes
Discovered (in 1897) that currents are streams of negatively charged particles he called electrons.
He thought that atoms must be composed of smaller particles – a mind boggling idea at the time!

9. Thomson’s “Raisin Bun” Model of the Atom
Atom is a positively charged ball studded with negatively charged electrons

10. Thomson’s raisin bun model didn’t last long, as it was quickly followed by a new model proposed by a scientist from New Zealand…
Ernest Rutherford

11. Ernest Rutherford (1871 – 1937)
Expected alpha particles to pass straight through
But every once in a while, a particle was reflected back!

12. Rutherford had discovered the nucleus!
The tiny, dense, positively charged centre of the atom.
10 years later he determined that the nucleus was actually made up of 2 types of particles:
A proton – positively charged particle
A neutron – particle with no charge

13. Niels Bohr (1885 – 1962) A Danish physicist who worked for Rutherford
He studied the parts of the atom surrounding the nucleus
Bohr was particularly interested in the electrons that existed in this space

14. He studied light given off by gases that glowed when an electric current was passed through them
He discovered that electron surround the nucleus in specific energy ‘levels’ or ‘shells’

15. Bohr’s Model: Electrons have different amounts of energy
Basically, electrons orbit the nucleus on specific paths
If energy is supplied, they can jump to higher energy level paths
When the energy supply stops, the electrons ‘fall’ back to their original path

16. Inside the Atom…
An atom is the smallest particle of an element that retains the properties of the element
Atoms are made up of 3 types of subatomic particles:
Proton (positively charged, found in the nucleus)
Neutron (no charge, found in the nucleus)
Electron (negatively charged, found outside of the
nucleus)

17. The Subatomic Particles
The nucleus contains protons and neutrons
It is extremely tiny but incredibly dense
Takes up 0.01% of the space in an atom but accounts for 99% of the mass!
Electrons have almost no mass but take up a huge amount of space (99.99% of the atom)