1. Honors Chemistry Section 4.1
The Development of a new atomic model

2. Rutherford’s Atom Major Advance
Did not explain all properties of the atom
Proton-electron attraction
Why didn’t atom collapse?

3. Light and Electrons Early 1900’s – light is a wave
Visible Light – Electromagnetic Radiation
Electromagnetic Spectrum

4. Electromagnetic Radiation
Moves at speed of light (c) = 3.0 x 108 m/sec
Wave Properties
Frequency – (ν) number of waves that pass a point in a given amount of time (cycles/sec, waves/sec, sec-1, Hertz)
Wavelength – (λ) distance from a point on one wave to the same point on the next wave.

5. Relationship between Frequency and Wavelength

6. Photoelectric Effect Early 1900’s This effect related to ν
If wave this not the case
Explained by Max Planck
Planck studied emission of light from hot objects
Said light emitted in small packets called quanta

7. Planck’s Equation E = hν h = 6.626 x 10-34 Joules ･seconds
Joule – unit of energy
E = Energy
ν = frequency

8. Einstein Dual Wave-Particle nature of electromagnetic radiation
Light can act both like a wave and like a stream of particles
Particles called photons.
Photon – particle of electromagnetic radiation with zero mass and carrying a quantum (packet) of energy
Photoelectric effect – electromagnetic radiation only absorbed in whole numbers of photons.
Eject an electron by hitting it with a photon with enough energy to free electron

9. Photons Increase ν increase E Must have minimum ν to get minimum E
Different metals require different minimum ν
DEMO – Energy in Photons

10. Spectra
Pass electricity through gas at low pressure – increase PE of gas
Lowest energy state – ground state
Higher PE state – excited state
When an excited atom returns to ground state it releases energy as electromagnetic radiation

11. Hydrogen’s Emission Spectrum

12. Quantum Theory Line emission spectrum Bright line spectrum 3 series
Lyman
Balmer
Paschen
Expected continuous spectrum
New model – Quantum Theory

13. Hydrogen’s Emission Spectrum

14. Emission and Absorption

15. Cont.

16. Demos/DVD’s
Gas Discharge Tube
Bohr Model
Spectra

17. Bohr Model Only works for hydrogen
Cannot explain spectra of multi-electron atoms
Cannot explain chemical behavior of atoms
What is next????