1. o We use models to help us understand things that are too: BIG small Fast s l o w or complicated to see in “real life”

2.  Scientists have used the results of experiments to help them create a model of the atom.  The atomic model has undergone many changes, and continues to develop and change… from THISto THIS

3.  Ancient Greek philosopher (460 – 370 BC)  Suggested that matter cannot be cut into smaller pieces forever  Gave a name to the smallest particle of matter: the ATOM ατομοσ

4.  Dalton was an English schoolteacher  Began teaching mathematics and chemistry at the age of 12  Revived the idea of Democritus’ “smallest piece” of matter

5.  “All matter is made of tiny particles called “atoms”  Atoms are indivisible and indestructible  Atoms of the same element are identical  Atoms of different elements differ in some fundamental way  Atoms combine in simple whole number ratios to form compounds These wooden balls, were the first models made to represent atoms - used by John Dalton to demonstrate atomic theory.

6.  English physicist  Worked with Cathode-Ray Tubes (CRTs)  Credited with the discovery of the electron Call me “JJ”

7.  Mysterious particles emanated from the cathode end  These particles were deflected by magnetic and electric fields  They were very small and negatively charged These particles were called “electrons” and were assumed to be a part of all matter

8.  The “Plum Pudding” model:

9.  New Zealand-born (1871 – 1937), student of JJ Thomson  Famous “Gold Foil Experiment”  Discovered that atom has a small, positive NUCLEUS with negative electrons moving around it - mostly empty space.

11. “ It was quite the most incredible event that ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you! ”

13.  Used Max Planck’s quantum theory to show that…  Electrons exist in different “energy levels”

14.  Electron “clouds” and “orbitals”

15.  A fellow researcher with Rutherford  Discovered years later that the nucleus contained not one, but TWO types of particles  This second particle was called the “neutron” because it had no electrical charge … mmmm, neutrons …

16.  Small, dense nucleus made up of….  positive protons, neutral neutrons, with  negative electrons, in “orbit” around nucleus

17.  Democritus – ATOMOS  Dalton – atoms as “solid balls”  Thomson – “plum pudding” model, with negative electrons  Rutherford – small positive nucleus, atom is mostly empty space  Chadwick – Nucleus contains protons and neutrons