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. Q. 19: Analyzing Emission Spectra
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 to absolute zero.
T0 = -273o C
Temp F C K
Abs. Zero –459 –
Freezing
Room
Boiling
Sun
TK = TC + 273
300 K is comfortable

8. Temperature must be in Kelvin (K)!
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, the higher 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 F =T4 2900 K 4500 K 5500 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
5500 K
F =T4
Flux is brightness over area
10,000 K
20,000 K

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