Honors Chemistry Section 4.1 The Development of a new atomic model

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

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

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.

Relationship between Frequency and Wavelength

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

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

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

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

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

Hydrogen’s Emission Spectrum

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

Hydrogen’s Emission Spectrum

Emission and Absorption

Cont.

Demos/DVD’s Gas Discharge Tube Bohr Model Spectra

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