6 Heisenberg Uncertainty Principle An electron’s location and speed cannot be determined at the same time.If we cause change to find one variable, we are no longer looking at the actual e- situation.If we need to slow or stop it to locate it or if we need to locate it to find its speed, then we allow the chance of change.So quantum mechanics can tell us the probability that an electron is somewhere, but it does not tell us how it got there.
7 Nodal SurfacesA nodal surface is a region that defines the border of an orbital. This is where the probability function equals zero. Electrons CAN NOT exist in this area.Nodal surfaces are NOT spherical for other orbitals.Nodal surfaces are spherical for the “s” orbitals.2p orbital3s orbital
15 Max PlanckMax Planck mathematically determined “h” that could be multiplied by to solve for energy (E) every time an electron gave off light as it fell. (This simply means that all wavelengths are proportional)E = h
18 Bohr ModelBohr was able to calculate the energy for the allowed orbits of the hydrogen atom using the formula:Since this is true of any level, Bohr postulated the energy between energy levels could be calculated as well:
19 Principle Energy Level (n) Bohr ModelEmission Spectraexplains HydrogenElectrons exist in quantized energy levelsAs electrons ‘drop’ to lower energy levels emitting quanta of energywhich translate to frequencies & wavelengthsEnergy (Joules)Principle Energy Level (n)Ratio of Level 1:Level X-2.18E-181-5.45E-1924E-1939E-1916-8.72E-20525E-20636E-20749
20 Energy of ElectronsWe can calculate the energy the electrons of a hydrogen atom emits when they fall by using the Balmer equationSo if an electron falls from the 3rd energy level to the 2nd energy level then –Note: energy levels are not actually distances between electrons and the nucleus.
25 Bright-line SpectraAtoms are quantized, existing only in definite energy stateswhen an atom absorbs a specific quanta of energy electrons jump to higher energy levels.An “EXCITED” electron jumps from its ground state to a higher energy level.The energy cannot be maintained so it falls back to where it came from losing exactly the same amount of energy that it absorbed.
26 De Broglie Small matter (electrons) have wavelike properties as well. Changed the Bohr model so that all elements could be explained according to their frequencies of energy.Remember that energy is constant and that standing waves are quantized as well (they only increase by multiples of ½)
27 De BroglieEssentially the model went fromde BroglieBohrto
28 de Broglie and Wave Model An electron in its path is associated with a wavelength.The wavelength depends on the mass:
29 Example ProblemWhat is the characteristic wavelength of an electron with a velocity of 5.97 x 106 m/s? (Use 9.11 x kg for the mass of an e-)