The Electrons can only orbit on specific orbits These orbits have specific energies

1. The Bohr Model of Atoms • The Electrons can only orbit on specific orbits • These orbits have specific energies • When an electron falls “down” energy is released in the form of a photon • If a passing photon has just the right energy, an electron can get bumped “up” • Because the electrons can only be on certain special energy levels, only certain amounts of energy can be absorbed/emitted • The special energies that can be absorbed or emitted depends on which type of atom you have

2. Emission Spectra of the Elements

3. The Quantum Mechanics of Atoms • Electrons don’t exist at one place at all – they are in a nebulous probability cloud • The Bohr model is simpler, so we’ll pretend it’s right electron cloud

4. Atomic Spectra • Suppose you take an atom and bump the electrons up (by heating it, for example). What type of light comes out? • Spectrum consists of emission lines • Exactly which lines tells you the kind of atom, like a fingerprint Q. 19: Analyzing Emission Spectra

5. Atomic Spectra • Suppose you take an atom and shine a bright white light on it. What does the spectrum of the light look like when it comes out? • Initial spectrum is continuous • Atom absorbs certain very specific frequencies • The same frequencies you saw before

6. Hot Stuff Heat • Heat is disorganized energy • Kinetic energy is organized motion – like all the air in the room moving the same way • If you make all the atoms in the room move different ways, you heat up the room • Whenever energy gets completely randomized, turned into heat, we say it is in thermal equilibrium • There is a statistical tendency for things to get disorganized

7. Temperature – the Kelvin Scale • Heat is disorganized energy. Temperature is a measure of how much heat there is. • If you have no disorganized energy,you are at Absolute Zero • Absolute Zero: -273oC • Kelvin - just like Celsius,but the zero is shifted toabsolute zero. T0 = -273o C Temp. F C K Abs. Zero –459 –273 0 Freezing 32 0 273 Room 70 21 294 Boiling 212 100 373 Sun 9900 5500 5800 TK = TC + 273 • 300 K is comfortable

8. Ideal Gasses • In a gas, all the atoms (or molecules) bounce around randomly. • The hotter it is, the faster they bounce around • As they bounce, they collide with the walls • Collisions cause pressure • The more atoms, and the hotter, thehigher the pressure P Pressure n Number density T Temperature (K) k constant P = knT Q. 19: Ideal Gas Law Temperature must be in Kelvin (K)!

9. Black Body Radiation Flux is brightnessover area F =T4 2900 K • All Objects give off electromagnetic radiation “light” • Some objects are (nearly) perfect absorbers, and perfect emitters. Such objects are called black bodies • Color and brightness of light depends on temperature 4500 K 5500K 10,000K 20,000K

10. Black Body Radiation lmaxT = 2900 Km • T in Kelvin Q. 20: Using Wien’s Law

11. Kirchoff’s Laws • Hot thick solid, liquid, or gas – Continuous spectrum • Thin gas – bright line spectrum • Thin gas with hotter thick gas behind it – dark line spectrum

12. Kirchoff’s Laws Continuous Spectrum: Hot, thick solid, liquid, or gas Bright Line Spectrum: Hot, thin gas Dark Line Spectrum: Cooler gas in front of hot, thick solid, liquid, or gas