Interpretation of Hydrogen Emission Spectra

White Light Spectrum (Wide Range of Colors and hence Energies of light)

Spectral lines of Helium (left) and Neon (right)

Hydrogen Emission Spectra Experiment – Experimental Observations Energy added in the form of heat, electricity or light → only certain specific colors of light are emitted

Interpretation of Hydrogen Line Spectra- Experimental Observations Since ONLY CERTAIN SPECIFIC COLORS OF LIGHT ARE EMITTED, ONLY CERTAIN SPECIFIC FREQUENCIES AND WAVELENGTHS ARE EMITTED Longer wavelengths – like red, have lower energy Shorter wavelengths – like blue have higher energy Specific colors = ONLY SPECIFIC ENERGIES OF LIGHT ARE EMITTED

Bohr Model If no restrictions on electrons’ energy and motion e- would pulled into nucleus- this does not happen; therefore there must be restrictions. Quantized- means restricted: only certain, specific values are possible Analogies: Nonquantized = ramp Quantized = stairs

Link to Hydrogen model’s phet

Postulates of Bohr model Electrons can have only certain specific values of energy. Electrons travel in fixed, circular orbits* When an electron absorbs the exact difference in energy between 2 levels it makes a quantum leap up When an electron makes a quantum leap down it releases the exact difference in energy between two levels. * = we no longer believe this postulate

Bohr model of Atom Historically important – first model of atom to introduce concept of quantized energy levels to explain hydrogen emission spectral lines Model was unable to explain all details hydrogen spectrum and very poorly predicts spectra of heavier elements Fatal flaw = oversimplified: e- don’t travel in fixed circular orbits

Link to Electron Orbits

Interpretation of Experiment Energy added to atoms is absorbed by ELECTRONS. Electron absorbs specific quantity of energy, it makes a quantum leap from its lowest energy GROUND state to higher energy EXCITED state.

Quantum Leaps: Ground → Excited Add Energy electron = ↑ n = 3 ___________ excited state n=2 ___________ excited state n=1 ↑ ____________ ground state

Quantum Leaps: Ground → Excited Add Energy electron = ↑ n = 3 ___________ excited state n=2 ↑ ___________ excited state n=1 ____________ ground state

Quantum Leaps: Ground → Excited Add Energy electron = ↑ n = 3 ___________ excited state n=2 ↑ ___________ excited state n=1 ____________ ground state

Back Page Electrons CANNOT remain in an excited state for any significant time period. Electron in excited state returns to the ground state by emitting a specific amount of energy in the form of LIGHT. Because only certain specific jumps from excited to ground state are possible, only certain specific energies and hence colors of light can be emitted.

Quantum Leaps: Excited → Ground Release of Light n = 3 ___________ excited state n=2 ↑ ___________ excited state n=1 ____________ ground state

Quantum Leaps: Excited → Ground Release of Light n = 3 ___________ excited state n=2 ___________ excited state n=1 ↑ ____________ ground state

Link to Hydrogen Emission Spectrum Animation

Link to Neon light PhEt applet

Link to lasers phet

Sodium Line Emission Spectrum