L> Spectral LinesIf we look at the spectrum the the Sun, we don"t just seecontinuous blackbody radiation -- we view dark linesas well.in 1860, Kirchhoff and Bunsen had actually been researching the spectralproperties of matter and noted that few of the dark lines in the sun wereat the exact same wavelength as bright lines created when salt was heatedup -- there need to be sodium in the Sun.Furthermore, they likewise published what space now well-known asKirchhoff"s Laws:A hot, thick gas or solid thing produces a continuous spectrumwith no dark spectral lines.A hot, diffuse gas produces bright spectral present (emissionlines)A cool, diffuse gas in front of a source of continuous radiationproduces dark spectral currently (absorption lines)in the consistent spectrum.What is walk on here?To understand this, we require two concepts: photonsand atom structurePhotonsWe have actually talked about how irradiate is an electromagnetic wave.It can be defined by wavelengthand frequency. Various wavelengthscorrespond to different colors, and also ultimately different species of radiation(UV, IR, radio, X-rays, etc).Light can likewise be identified by discrete particlescalled photons -- thus the wave-particleduality of light.How much power is included in a single photon?How quick does it move? exactly how muchmass does the have?How was this discovered? Via thephotoelectric effect:It had been i found it thatwhen light shines top top a steel surface, electrons space ejected from the surfacewith a characteristics kinetic energy. If you rise the brightness ofthe light, friend get more ejected electrons, but not at greater kinetic energies.So even though you space bathing themetal in much more energy, the electrons coming off have the very same maximum energy.Einstein explained this by suggestinglight was comprised of discrete particles -- photons -- that had actually a discreteamount the energy. More photons might eject more electrons, yet not at higherspeeds. This is what Einstein won the 1921 Nobel prize for, no hiswork ~ above special and also general relativity.Example: just how much energy doesa solitary blue (4000 Angstrom) photon have? here is a quick tip come remember:hc=12400 eV A.So one 4000 A photon has 12400/4000=3.1eV of energy.Atomic StructureAt atom is make of a nucleus (protons and neutrons) withelectrons "orbiting" around it. Quantum mechanicssays that these electroncs can not orbit with any kind of energy castle like, butmust live in ~ discrete, well-defined energy levels.Consider the hydrogen atom - 1 electron in orbit around1 proton. Simple!The permitted energy levelsin the hydrogen atom are offered byIf the electron is in the n=1state, the power is -13.6 eV and also itis referred to as the floor state of the atomIf the electron is in the n=2state, the energy is -3.4 eV and itis dubbed the an initial excited state ofthe atomThink of this visually, in terms of orbits (this is no reallycorrect, but it is a valuable analogy...)Now, what would take place if an electron moved from one levelto another? The power of the atom would change! Howcould this happen?If an electron moves approximately a higherstate, the atom have to have acquired energy, by taking in a photon. Yet itcan"t absorb any kind of old photon, it need to absorb one with specifically the rightenergy. Therefore if you want to move from n=1 to n=2, the energy distinction is13.6 eV - 3.4 eV = 10.2 eV. What photon has precisely that energy? One witha wavelength that 1216 A.If one electron moves under from a higherstate, the atom loser energy, for this reason it should emit a photon. However again, onlya photon i m sorry carries away the precise amount of energy difference.


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If theelectron to be going native n=2 to n=1, it would emit a photon of 1216 A.In the hydrogen atom, transitions to/fromthe n=2 level indicate energies which exchange mail to optical photons. Thesetransitions were the very first discovered, and are called the Balmer series.TransitionNameWavelengthn=3 to/from n=2Halpha6563 An=4 to/from n=2Hbeta4861 An=5 to/from n=2Hgamma4340 An=6 to/from n=2Hdelta4102 AThe firstfour Balmer linesOther series includetransitions to/from the floor state(n=1): The Lyman seriestransitions to/from the n=3 state:The Paschen seriesHere is an energy level diagram forthe hydrogen atom:Enough rash -- show us a real spectrum! Okay,here is a spectrum the a hot, blue star referred to as an A star.(courtesy Diamond Dave Silva)Wow! Look in ~ those Balmerlines!