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Atomic Spectra and Electron Orbitals The Classical Atom Electrons orbited the nucleus. Problem!! Accelerating charges emit radiation (energy) With less energy the electron orbitals should shrink and the electrons should spiral into the nucleus The Bohr Atom Electrons orbit in specific energy levels without radiating Each energy level has a specific energy To change energy levels, atoms must either absorb or emit energy (photons) Link Ground State vs. Excited States Ground state is the lowest energy level in the atom. All other energy levels are known as excited states. Quantization of Energy A result of the Bohr atom is that energy cannot come in any amount it wants, it must be in specific amounts of energy called quanta Like steps or rungs of a ladder Electron Volts (eV) The energies involved in atomic spectra are very small, making it inconvenient to use Joules as our units of energy 1 eV = 1.6x10-19 J eV J J eV multiply by 1.6x10-19 divide by 1.6x10-19 Hydrogen Atom: Energy Levels and Energies of Transition 13.6eV E 2 n E = -2.176 x 10-18 J n2 1 1 E 13.6eV 2 2 n n i f n - energy level of atom primary quantum number n = 1, 2, 3, … Photon Energy E = hf = hc/l h = 6.626 x 10-34 J*s c = 3x108 m/s f – frequency l – wavelength Ephoton = Eatom Eatom > 0 if atom absorbs photon Eatom < 0 if atom emits photon Emission Spectra The set of energies emitted by an atom. Energy determines frequency which determine color Electromagnetic Spectrum Absorption Spectrum How we know the gaseous atmosphere surrounding the sun Spectral Series Spectral series are the set of energies produced when electrons from excited states emit photons and transition down to the same final energy level Three important series for Hydrogen: Lyman Series: nf = 1 Ballmer Series: nf = 2 Paschen Series: nf = 3 Atoms that aren’t Hydrogen The formulae in the previous slides only apply to Hydrogen. For other atoms, the energies cannot be so easily calculated, and will often be given to you directly. Energy Level Diagram E = Ef - Ei Ionization Energy In order to remove an electron from an atom you have to add enough energy make the energy zero. i.e. if you are at ground level and have an energy of -10.38eV that means you need 10.38eV if energy to ionize All left over Energy become Kinetic Energy Example An atom’s only electron is in the fourth energy level (-2.35 eV). How many different photon energies can be emitted as this photon returns to the ground state (-15.8 eV)? What is the frequency of the photon that would be emitted if the electron returned to the ground state in a single transition?