The Horsehead and the Orion NebulaCourse AnnouncementsAssignmentsLight as a Particle - PhotonsThe Energy of PhotonAtomic StructureAtomic StructureAtomic StructureAtomic StructureAtomic StructurePhotons + AtomsFormation of spectral linesThe Hydrogen Atom (1 proton, 1 electron)Spectrum of HydrogenHydrogen Energy DiagramSpectrum of HydrogenExample Hydrogen Lines QuestionExample Hydrogen Lines QuestionKirchhoff’s Laws ExplainedUnderstanding Kirchhoff’s LawsUnderstanding Kirchhoff’s LawsUnderstanding Kirchhoff’s LawsUnderstanding Kirchhoff’s LawsAtoms heavier than HydrogenAtoms heavier than HydrogenSpectrum of an Emission NebulaMolecular LinesMolecular LinesMolecular LinesSpectral Line AnalysisSpectral ThermometerRadial VelocityLine BroadeningThermal Broadening - TemperatureCollisional/Pressure BroadeningRotational BroadeningMagnetic Field BroadeningThe Horsehead and the Orion NebulaCredit: Roberto Colombari & Federico PellicciaCourse Announcements•Quiz 2 at end of class today•Exam 1 will take place Wednesday, 28 Sept.–Will cover Chapters 1 – 4–Will release study materials throughout the week.AssignmentsReading Assignments•No new readingParallel Lectures•No new parallel lecturesMastering Astronomy•Chapter 3 Homework[Due Monday, 19 Sept. at 11:59 PM EDT]•Chapter 4 Homework[Due Monday, 26 Sept. at 11:59 PM EDT]Light as a Particle - PhotonsLight comes in discrete packets called photons… a particle•A particle of light, a photon, is a distinct packet (quantum) of light, and it carries a very distinct energy. Photons are packets (quanta) of EM waves that behave as particles, where h is the Planck Constant = 6.626 x 10-32 J s (Joule seconds) Photon energy usually measured in electron volts (eV), which is the energy gained by an electron accelerated through an electric potential of one volt. 1 eV = 1.60 x 10-19 J (Joules)For a UV photon with E = 10.2 eVUsing a more precise versionFor a red photon with E = 1.9 eVThe Energy of Photon•As a particle, a photon has an energy that is directly proportional to frequency (inversely proportional to wavelength)=Shorter Wavelengths“Bluer”HIGHER ENERGYLonger Wavelengths“Redder”LOWER ENERGYRadio MicrowaveIRVisibleUVX-rayGamma RayAtomic Structure•Electrons ‘orbit’ the nucleus at distinct energy levels called orbitals.–Not like planetary orbits, which can orbit at any distance (or rather, energy)•The lowest energy level, n = 1, is called the Ground State•Electrons prefer to be in the Ground State, which is the lowest energy state.The outdated, but useful, Bohr ModelBohr Model of Hydrogen, HWith energy levelsHydrogen, H1 proton + 1 electronAtomic StructureThe outdated, but useful, Bohr Model•To move to a higher energy level, i.e., further from the nucleus of the atom, the electron needs additional energy.•Electrons with higher energy ‘jump’ to a more energetic (n > 1) state: an excited state.•Label excited states as first excited state (n = 2), second excited state (n = 3), …, nth excited stateBohr Model of Hydrogen, HWith energy levelsHydrogen, H1 proton + 1 electronAtomic StructureThe outdated, but useful, Bohr Model•First ‘jump’ (ground state to first excited state) requires the most energy. Each subsequent jump (n=2 -> n=3; n=3 -> n=4) requires less energy to excite the electron•Again: Every ‘jump’ to a higher energy level requires a specific energyBohr Model of Hydrogen, HWith energy levelsHydrogen, H1 proton + 1 electronAtomic StructureThe outdated, but useful, Bohr Model•There is a maximum energy that an electron can have and still be a part of the atom.•If an electron achieves or exceeds that maximum energy, it is no longer bound to the nucleus, and the atom is said to be ionized.•An atom missing one or more of its electrons is called an ion.Electron no longer boundAtomic StructureA more realistic viewElectrons are nor really on ‘orbits’ like in the Bohr Model, but rather, occupy specific volumes of space around the nucleus called Orbitals. The location of an electron in an orbitals has a probabilistic nature.These S, P, D, and F orbitals and quantum mechanics make sense of the period table of elementsPhotons + AtomsPhotons and quantized energy•Each electron orbital has an associated specific, quantized, energy E–No ‘in-between’ levels•Absorption and Emission Spectra of hydrogen, and other atoms, demonstrated that atoms can only absorb or emit specific energies.•The amount of energy E absorbed or emitted corresponds perfectly to the energy difference between two electron orbitals•These packets of quantized energy are particles called photons, with energy E = constant x frequency of lightΔE = h(c/λ)h = Planck’s constantFormation of spectral linesMultiple paths of excitation and de-excitationDirect excitation and de-excitation back to Ground StateCascade De-excitationRed glow due to the decay of a 2nd Excited State (n = 3) to 1st Excited State (n = 2) of HydrogenFlourescenceThe Hydrogen Atom (1 proton, 1 electron)Energy levels of the hydrogen atom, showing two series of emission lines:The energies of the electrons in each orbit are given by:The emission lines correspond to the energy differences2113.6 1 -- eV.nEn� �=� �� �Spectrum of HydrogenSpectral SeriesLyman SeriesTransitions starting or ending at the Ground State (n =1)-Ultraviolet Lines-Lα = 121.6 nmBalmer SeriesTransitions starting or ending at the 1st Excited State (n =2)-Visible Lines-Hα = 656.3 nmHydrogen Energy DiagramSpectral SeriesUltraviolet (UV)PhotonsVisible LightPhotonsSpectrum of HydrogenThe Balmer Series – Visible Light Emission/AbsorptionHydrogen Alpha - HαHydrogen Beta - Hβ Hγ HδExample Hydrogen Lines QuestionThe Balmer Series line, Hydrogen Alpha, will be seen as an absorption line when the electron in the hydrogen atom makes which electronic transition?A. 1st Excited State to Ground State (n = 2 -> 1)B. Ground State to 1st Excited State (n = 1 -> 2)C. 2nd Excited State to Ground State (n = 3 -> 1)D. Ground State to 2nd Excited State (n = 1 -> 3)E. 2nd Excited State to 1st Excited State (n=3-> 2)F. 1st Excited State to 2nd Excited State (n=2-> 3)Example Hydrogen Lines QuestionThe Balmer Series line, Hydrogen Alpha, will be seen as an absorption line when the electron in the hydrogen atom makes which electronic transition?A. 1st Excited State to Ground State (n = 2 -> 1)B. Ground State to 1st Excited State (n = 1 -> 2)C. 2nd Excited State to Ground
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