CHM135H1 Lecture Notes - Lecture 4: Bohr Model, Photon, Magnetic Quantum Number
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Published on 14 Sep 2018
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CHM135 – LECTURE 4: Electronic Structure of Matter
September 14, 2018 (Relevant Reading – Chemistry 7ed McMurry/Fay/Robinson, Chapter 5)
Atomic Line Spectra
- In the experiment, there’s hydrogen gas inside an element where the atoms are excited
electrically and emits light as the electrons in the atoms fall back into lower energy
levels; the light emitted comes through a narrowed slit and dispersed by a prism to create
a line spectrum
- Excited atoms give off only discrete frequencies of light
- Exact frequencies are different for different elements
- Provides evidence for:
o Electrons having certain energy levels in atoms
o Light emitted corresponds to energy differences between levels
o Conservation of energy
Bohr Model of Atom: Quantized Energy
-
; m and n are the integer of shell, where n > m and R = 1.097 x 10-2 nm-1
- Bohr model gets energy calculation right and the idea of orbit levels right
- Problems with Bohr Model:
o 1) only works to explain spectra of 1-electron systems
o 2) doesn’t accurately predict electron location
Nature of Light
- Wave nature
o Interference, diffraction
- Particle Nature
o Photoelectric effect
Nature of Electrons
- Particle Nature
o Fixed mass and charge
▪ me = .1 x 10-31 kg
▪ charge = 1.6 x 10-19 C
- Wave Nature
o Experimentally – diffraction
▪ It was shown experimentally that electrons behave as waves
• Electrons were shot at a nickel crystal and a detection screen found
the electrons to be scattered into a diffraction pattern; behaving as
waves
o Wavelength of electron
▪ E =
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