1. Chapter 3 The History of the Atom

2. I. The Scientists and their Discoveries A.Democritus 1. Date = 400 B.C 2. Discovery = Theorized the smallest unit of an element 3. Importance = gave the term and definition of atom

3. Democritus ATOM Smallest particle

4. B. John Dalton 1. Date = 1803 2. Discovery = a. Every element is made of atoms b. atoms of same element exactly the same c. Atoms of different elements join together to form molecules

5. 3. Importance = proposed the ATOMIC THEORY Atomic Theory = 1. everything is made up of atoms 2. atoms make up molecules 3. atoms of the same element are the same

6. Molecules made of atoms John Dalton Atomic Theory

7. C. J.J. Thomson 1. Date = 1898 2. Discovery = a. discovered electrons b. electrons are negative 3. Importance = atoms have both negative and positive particles

8. J.J. Thomson “Plum Pudding” model Electrons are negative

9. D. Ernest Rutherford 1. Date = 1911 2. Discovery = a. discovered nucleus b. did a “gold foil” experiment c. atoms mostly made of space 3. Importance = a. nucleus is very tiny, and positively charged b. electrons outside of nucleus

10. Ernest Rutherford Gold Foil Experiment Electrons outside nucleus Discovered nucleus

11. E. Niels Bohr 1. Date = 1913 2. Discovery = a. Electrons are in energy levels b. s, p, d, f orbitals c. 1 st = 2 electrons; 2 nd = 8 electrons; 3 rd = 18 electrons 4 th = 32 electrons

12. 3. Importance = electrons orbit around nucleus in a certain pathway This is the Bohr Model

13. Niels Bohr Electrons in energy levels

14. F. Schrödinger 1. Date = present 2. Discovery = electrons are impossible to find ( a moving fan) 3. Importance = a. Atoms are neutral b. atoms must have the same number of protons and electrons

15. Schrödinger Atoms have no charge Same number of protons and electrons

16. II. The Mass of Atom A. Protons 1. are positively charge 2. have a mass of 1.67 X 10 -27 kg 3. Found in the nucleus B. Neutrons 1. Neutral 2. have a mass of 1.67 X 10 -27 kg 3. Found in the nucleus

17. C. Electrons 1. are negatively charged 2. Have a mass of 9.11 X 10 -31 kg = 0 atom mass 3. Found orbiting outside the nucleus, so their mass does not effect the atom’s mass!

18. Section Question 1.Which scientist gave us the word atom? 2. Which scientist made up the atomic theory? 3. Every element is made of atoms, atoms of the same element are exactly the same, different atoms make up molecules. These statements make up the what?

19. 4. Which scientist discovered the electrons? 5. Which scientist discovered the nucleus? 6. Which scientist discovered that electrons where in energy levels? 7. Which scientist said atoms where neutral because they had equal number of protons and electrons?

20. 8. What is the mass of protons? 9. What is the mass of neutrons? 10. What is the mass of electrons? 11. Which part of the atom has the least amount of mass?