1. The Atom

2. Dalton’s Atomic Theory 1.Elements are made of tiny particles called atoms. 2.All atoms of a given element are identical. 3.The atoms of a given element are different from those of any other element. 4.Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms. 5.Atoms are indivisible in chemical process. Atoms are not created nor destroyed.

3. Which numbers in Dalton’s Atomic theory are no longer valid? 2. All atoms of a given element are identical. Why not? 5. Atoms are indivisible in chemical process. Atoms are not created nor destroyed. Why not? Isotopes We can split an atom

4. Subatomic Particles Thomson’s experiment Discovered electrons are negative (cathode ray tube and a magnet) Plum pudding model of atom Had negatives and positive all mixed together

5. Rutherford’s experiment Shot alpha particles at thin sheet of gold foil. All of the particles should have passed through, but some bounced back. (like shooting a cannon ball at a sheet of paper and having it bounce back) Discovered the Nucleus Contains: http://micro.magnet.fsu.edu/electromag/java/r utherford/ Small dense core of an atom Protons (+) and neutron (neutral)

6. Modern Atomic Model Nucleus: in the middle Protons: Mass = 1 a.m.u. (+) charge Neutrons: Mass = 1 a.m.u. neutral Electron cloud surrounds nucleus Electrons: Mass = 0 (-) charge

7. Symbols of Atoms Atomic mass at. mass =(#p+) + (#n) Atomic number at. # = number of protons Symbol of element

8. Isotopes Atoms of the same element with different number of neutrons. p + = n = e - = 6 6 66 6 8 carbon - 12carbon - 14

9. Isotope Symbol Examples Symbol at. number at. Mass # p+ # n # e - 36 198 2657263126 7911979 351817 4635 17 79 17 3581