1. Modern Physics
The Atom

2. What is physics really about
Mechanics we look at interactions between bodies
Electricity and magnetism we look at interactions between charges
Waves and light are about the transfer of energy
Mass
Charge
Energy

3. What is matter (the stuff around us)
If you took a lump of matter, could you keep on dividing it in two or would you get to a piece so small that you couldn’t divide any further?
The greeks deicded you couldn’t – they called the smallest particle an atom (the greek word for indivisible)

4. Aristotle
The greeks thought all matter made of earth, air, fire and water
Eg lead was a mixture of these so if you could change the mixture
You could turn gold into lead!

5. 1800 Compunds were known about
Dalton came up with the idea that compounds were made up of atoms
Lead and gold atoms different so could not change lead to gold

6. 1910 Thompson came up with plum pudding model for the atom
Knew about electrons (the plums) and said the dough was positive
Matter is mass, charge and energy!

7. 1911 – NZ’s Rutherford
Gold foil experiment using alpha (+) particles (He nuclei) fired through very thin gold foil onto a zinc sulfide screen
Most particles went straight through but some scattered through a large angle

8. The details Rutherford considered
The large scattering of the alpha (+) particles suggested there was a large + charge at the centre of a gold atom
Gold is neutral so the electrons must be small and orbiting
The atom must be mostly empty space

9. Bohr
Bohr put the electrons into energy shells around the nucleus
Chadwick discovered the neutron in the nucleus
The model of the atom took 2000 years to design and we have had it about 70 years!

10. The atom is really more complex
But for Year 12 Physics – we don’t care!

11. Atomic notation Element symbol
Atomic number – give the number of protons in the nucleus and therefore the number of electrons in neutral atom
Mass number – how many particles in the nucleus

12. Isotopes – very important to nuclear physics
They are atoms that have the same number of protons but different numbers of neutrons
Heavier isotopes of an atom are unstable and are the most likely to decay or be involved in nuclear reactions