AP Chemistry Unit 3 - Elements

1. AP ChemistryUnit 3 - Elements Lesson 7 – Atomic Emission Spectra Book Section: 6.3

2. The Nature of Energy • Another mystery in the early 20th century involved the emission spectra observed from energy emitted by atoms and molecules.

3. The Nature of Energy • For atoms and molecules one does not observe a continuous spectrum, as one gets from a white light source. • Only a line spectrum of discrete wavelengths is observed.

4. The Nature of Energy • Niels Bohr adopted Planck’s assumption and explained these phenomena in this way: • 1. Electrons in an atom can only occupy certain orbits (corresponding to certain energies)

5. The Nature of Energy • Niels Bohr adopted Planck’s assumption and explained these phenomena in this way: • 2. Electrons in permitted orbits have specific, “allowed” energies; these energies will not be radiated from the atom.

6. The Nature of Energy • Niels Bohr adopted Planck’s assumption and explained these phenomena in this way: • 3. Energy is only absorbed or emitted in such a way as to move an electron from one “allowed” energy state to another, the energy is defined by E = hν

7. The Nature of Energy • The wavelength of light absorbed or emitted from the process of electron promotion or demotion can be calculated by the equation: • RH = Rydberg constant (1.096776 x 107 m-1) • n1,n2 = energy levels (whole numbers)

8. Sample Problem • Using the diagram, predict which of the following electronic transitions produces the spectral line having the longest wavelength: • n = 2 to n = 1 • n = 3 to n = 2 • n = 4 to n = 3

9. HW: 6.32, 34, 36, 40 • This Week: • Tuesday – Wave Nature of Matter (6.4-6.9) • Wednesday – Quantum Numbers (6.4-6.9) • Thursday – Gravimetric Analysis of a Chloride Salt, Quantitative Analysis of Soluble Sulfate Due • Friday – Electron Configurations (6.4-6.9) • 10/18 – Gravimetric Analysis of a Chloride Salt Due • 10/20 – Elements Exam • 10/21 – Problem Set 2 Due