Week of Monday November 13 th , 2006

1. Week of Monday November 13th, 2006 The atom Rutherford’s Problem Niels Bohr’s Solution

2. Monday November 13th, 2006 The atom Rutherford’s Problem Niels Bohr’s Atomic Model Bohr’s Problem Heisenberg’s Uncertainty Principle

3. Drill • Why don’t the nuclei of the atoms in your bottom touch the nuclei of atoms in the chair when you sit down? • Atomic # number means the # of ______ and when the atom is neutral, the atomic # will be the same as the # of _________. • Convert units: • 500 mL to ____________pL 13L = 13,000 ____ • 17 ms to ____________Ms 0.1m = 100 _____ • 3,001 mm to _______m 0.1 cm = 1 _____ Electrons repel each other. protons electrons 5 x 1011 500,000,000,000 mL 1.7 x 10-8 0.000 000 017 mm mm 3.001

4. Subatomic particles • Protons • Neutrons • Electrons Mass = 1/2000th of The mass of neutrons Or protons. All mass is in the nucleus

5. The world of the electron • Electrons move about the nucleus (protons & neutrons) • Electrons are exceedingly tiny • Rules are different for them • They live in the world of quantum mechanics • The line separating matter from energy blurs

6. Rutherford’s problem Rutherford thought: • Nucleus is positive (protons & neutrons) • Electrons are negative • Electrons orbit around nucleus like planets around the sun Questions that remain: • How do electrons manage to stay apart from nucleus (opposites attract)? • When you add energy to atoms, why do they give off light?

7. Niels Bohr’s Solution 1. Electrons can stay separate from nucleus if: • Electrons have their own energy that keeps them from getting sucked into nucleus Bohr tries to prove this by: • Predicting how much energy that is for each electron • Kinetic energy of each electron = KE = ½mv2 • Finding how far away those orbits are from nucleus They should orbit at very specific distances away from the nucleus for model to be stable 1885 - 1962

8. Bohr’s model of the atom Higher energy Levels are farther from nucleus. Lower energy Levels are closer to nucleus. nucleus Electron loses energy as it falls down an energy level hv is wavelength of light given off Electron orbitals/ energy levels

9. Niels Bohr’s Solution 2. Atoms give off light when they absorb energy because: • Each orbital = an energy level • Electrons can jump energy levels when energy is added to an atom • Electrons give off energy (light) when source of energy is taken away • Light wavelength depends on how far electrons fall 1885 - 1962

10. Bohr’s problem • Could not measure how fast electrons moved without losing their location. • Could not pinpoint electron location without losing information on their velocity.

11. Schrödinger’s theory • Thinks Bohr is wrong: • Electrons aren’t really matter, but waves of energy

12. Heisenberg’s Uncertainty Principle Quantum mechanics • Impossible to know both location & velocity of electron because observation involves using light. • Light will change location and velocity of electron because it adds energy! • What you can know is the probability of electron’s location & velocity • Electron orbital now  area where electron has a probability of being found • Answers the particle/wave argument

13. Atom in its neutral state • # protons • This is the way elements are shown in the PT = atomic # = # electrons

14. Normal (on earth) chemical rxns Atoms Δ # of electrons by • Stealing • Losing • Sharing with other atoms Δ means “change”

15. Nuclear Chemistry • If you Δ what is in the nucleus you are doing nuclear chemistry • Δ # protons  you have a new element • Δ # neutrons  radioactive decay Δ means “change”

16. Where do elements come from? While you are watching movie, write down no more than 4 words for each question. HW for tonight Rewrite your answers in complete sentences.

17. Niels Bohr