Atomic Spectra and Electron Orbitals

1. Atomic Spectra and Electron Orbitals

2. 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

3. 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

4. Ground State vs. Excited States • Ground state is the lowest energy level in the atom. • All other energy levels are known as excited states.

5. 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

6. 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 multiply by 1.6x10-19 • J  eV divide by 1.6x10-19

7. Hydrogen Atom: Energy Levels and Energies of Transition • n - energy level of atom • primary quantum number • n = 1, 2, 3, … E = -2.176 x 10-18 J n2

8. Photon Energy • E = hf = hc/l • h = 6.626 x 10-34 J*s • c = 3x108 m/s • f – frequency • l – wavelength • Ephoton = DEatom • DEatom > 0 if atom absorbs photon • DEatom < 0 if atom emits photon

9. Emission Spectra • The set of energies emitted by an atom. • Energy determines frequency which determine color

10. Electromagnetic Spectrum

11. Absorption Spectrum • How we know the gaseous atmosphere surrounding the sun

12. 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

14. 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.

15. Energy Level Diagram • DE = Ef - Ei

16. 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

17. 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?