1. C HAPTER 4 A TOMS AND THE P ERIODIC T ABLE Section 1 Atomic Structure p. 104

2. O BJECTIVES Analyze development of Atomic Theory Describe the subatomic particles and their behaviors

3. I.Atomic Theory sesdfAtomic Theory RapAtomic Theory Rap A. Democritus (300 BC- Greek) 1. Said universe was made of invisible units called atoms 2. Atom means unable to be divided B. John Dalton (school teacher 1808) 1. Agreed with Democritus but had evidence to support ideas (Atoms can’t be divided) 2. All atoms of an element are alike 3. Atoms join to form compounds

4. II. What is an atom? A. Nucleus 1. Proton a. Positive chargeb. Mass – 1 x 10 -27 kg 2. Neutron a. Neutral (no) charge b. Mass – 1 x 10 -27 kg B. Electron Cloud 1. If the nucleus was a marble the atom would be the size of a stadium 2. Electrons travel at near the speed of light 3. Negative charge with a mass of 9.11 x 10 -31 kg C. Unreacted atoms have no charge

5. III. Modern Models of the Atom A. Neils Bohr (1913- Denmark) 1. Electrons act like the planets in a solar system 2. Energy is determined by its path around the nucleus- must gain energy to move to a higher level B. 1925 – Bohr’s model no longer worked 1. Electrons act more like waves 2. Wave-Particle Duality of Nature (can act as both)

7. C. Quantum Theory (Model) 1. Electrons’ exact location cannot be known – Heisenberg’s Uncertainty Principle (You can’t observe something without changing it) 2. Electrons can exist in energy levels- 1st – 2 Electrons, 2nd – 8, 3rd – 18, 4th – 32 3. Electrons are found in orbitals in the energy levels- defined by shape (p. 109) a. S orbital – can have only 1 with a total of 2 electrons b. P orbital – can have 3 suborbitals with a total of 6 electrons

8. c. D orbital – can have 5 suborbitals with a total of 10 electrons d. F orbital – can have 7 suborbitals with a total of 14 electrons 4. Valence electrons a. Electrons in the outer most energy level (shell) b. It determines chemical properties and ability to bond c. Has the magic number of 8 (stability)