2 Atomic Theory Summary – the atom is the smallest particle of matter.
3 History of the Atom Cont. JJ Thomson (1897) – Raison Bun TheoryElectrons (negative) distributed in a positive sphereCathode Ray Tube used to measure themass of the electronErnest Rutherford (1911) – discovered that atoms have a positive nucleusGold Foil ExperimentPositive charge due to protons
4 James Chadwick (1932) – within the nucleus there are protons and neutrons (no charge) Niels Bohr – came up with the current model of the atom taught in Grade 9 and 10 Science; - Bohr Rutherford Model (planetary model)
5 Bohr-Rutherford Model Electrons move around the nucleus in circular paths called ORBITS / ENERGY LEVELSEach Orbit / energy level can hold a specific # of electrons (always fill the closest orbit first and work out from the nucleus)1st – 2, 2nd – 8, 3rd – 8, 4th – 18 ( )
7 Summary of the Three Subatomic Particles The Proton:- located inside the nucleus- is positively charged- symbol is p+The Neutron:- has no charge (neutral)- symbol is noThe Electron- orbits outside the nucleus- very tiny compared to the proton or neutron- is negatively charged- symbol is e-
8 Other Terms Atomic Number - the number of protons - unique to each atom, use it to identify an element Mass Number (Atomic Mass) - the number of protons plus the number of neutrons - measured in atomic mass units (amu)
9 Since atoms are neutral (ie Since atoms are neutral (ie. No charge), the number of protons in an atom must equal the number of electrons Summary Atomic # = #p+ = #e- Mass # = #p+ + #no