2. Atomic Theorists The ‘Who’s Who’ of the atomic world

3. Democritus One of the first atomic theories Matter is made up of small particles (atoms) and empty space “Atomos” are invisible

4. John Dalton 1803 ( and his theory) Elements are made of atoms Atoms of the same element are identical and indivisible Atoms combine in whole number ratios to form compounds Chemical reactions are the result of the rearrangement of atoms

5. Lavoisier late 1700’s Law of Conservation of Mass Matter is neither created or destroyed Proust 1799 Law of Constant composition Compounds always form the same way

6. Benjamin Franklin 1706-1790 Identified 2 types of electrical charge which he called positive and negative

7. Farraday Suggested that the structure of atoms was somehow related to electricity.

8. J. J. Thomson Using cathode ray tubes, he discovered the existence of a negatively charged particle in the atom Electron (e - ) His atomic model is called plum pudding because protons and electrons are scattered (like chocolate chip cookie)

9. Robert Millikan Using his oil drop experiment, he measured the charge of the electron

10. James Chadwick Discovered neutral particle in the atom Neutron (n°)

11. Becquerel Accidentally discovered radioactivity in 1892 by placing a rock on a piece of film. The rock had uranium in it. Marie & Pierre Curie Isolated radioactive elements

12. Ernest Rutherford Using his gold foil experiment, he discovered that there is a dense middle portion of an atom Nucleus Alpha and beta particles

13. Niels Bohr Presented a model of the atom that was accepted for many years The nucleus is the middle part of the atom, while the electrons ‘orbit’ the nucleus in fixed distances

14. Erwin Schrodinger Presented electron cloud model of the atom Electrons are found in regions outside the nucleus

15. Subatomic Particles Protons (p + ) have a positive charge and are located in the nucleus Electrons (e - ) have a negative charge and are located in orbitals outside of the nucleus Neutrons (n°) have neutral charge and are located inside the nucleus

16. Atomic Number Number of protons (p+) Number of electrons(e-) In a neutral atom, the number of protons and electrons is the same. Name Atomic Mass 6 C 12.011 Carbon Symbol Mass number is the SUM of protons and neutrons. What do the numbers and letters mean?

17. Figuring Out Subatomic Particles The ATOMIC NUMBER indicates the number of PROTONS and ELECTRONS in a neutral atom The MASS NUMBER is the sum of protons and neutrons How many neutrons are present in an atom of carbon with a mass number of 13? p + + n° = 13 Atomic number = #p + = 6 6 + n° = 13 n° = 7

18. Albert Einstein’s Lighter Side