1. Chemistry Science 10 History of the Atom

2. Atomic Theory  Answer the following questions How long has the Atomic Theory been around?How long has the Atomic Theory been around? Is the Atomic Theory the work of one scientist?Is the Atomic Theory the work of one scientist? Have there been many changes to the Atomic Theory?Have there been many changes to the Atomic Theory? Do you think we fully understand atomic behaviour?Do you think we fully understand atomic behaviour?

3. History of the Atom  Began with Democritus  Theory continually tested and refined through history until we have the current model

4. Democritus  460-370BC  Greek Philosopher  Pictured the atom as a solid sphere – hypothesised that there was a piece of matter that could no longer be divided in two  No real science

5. John Dalton  1766-1844  Hypothesised that there was a building block of matter  Gave it the name of an atom  Basically, he restated Democritus’s Theory based on scientific observation

6. John Dalton’s Theory  Matter was composed of atoms  Atoms of the same type all had similar mass  A pure substance would contain the same type of atoms  Compounds were different types of atoms combined together  Chemical reactions were the rearranging of compounds

7. JJ Thompson  1856-1940  Used electron beam directed at the atom to test behaviour Discovered that cathode rays were streams of electrons (negative particles)Discovered that cathode rays were streams of electrons (negative particles)  Discovered there are both positive and negative particles

8. JJ Thompson’s Theory  “Raisin-Bread” Model of the Atom Solid mass of positive charge (bread)Solid mass of positive charge (bread) Random electrons with negative charge throughout (raisins)Random electrons with negative charge throughout (raisins)  Attempted to predict number of electrons using electrostatic forces

9. Ernest Rutherford  1871-1937  Set out to test Thompson’s Model  Used alpha particles (radioactive) directed at Gold Foil  Proposed the Nuclear Model of the atom

10. Ernest Rutherford’s Model  All atoms would have a positive nucleus 99.9% of atom’s mass99.9% of atom’s mass Only.1% of atom’s sizeOnly.1% of atom’s size  Atoms would have orbiting electrons (like planets)  Majority of the atom is empty space

11. Neils Bohr  1885-1962  Tested planetary orbital model of atom  Used Hydrogen spectra for analysis

12. Neils Bohr’s Model  Discrete energy levels in which electron can exist  Electrons can move between levels but never have a non- whole number energy level  Quantization of energy

13. Quantum Mechanical Model  No longer individual science  Teams work together to solve problems  Current model explains why the periodic table works

14. Quarks & Leptons  Newest theory  Quarks make up protons and neutrons  Electrons are another type of matter called leptons  Bosons create forces