Exam Make up. Approximate make up Bit less than half Midterm 1, a bit more than a ¼ midterm 1, about ¼ midterm 2. Same format as before: Short answer: no partial credit Long answer: partial credit: more limited than the midterms, most of this is review material. You will be expected to do higher quality work.
Questions • What would happen in the photoelectric effect if light were simply a wave? • Energy of the waves would be dependent on intensity instead of on frequency. • What is the threshold frequency? • Minimum frequency (or ___________ wavelength) that still allows electrons to be ejected. • What happens if you increase intensity of light if you are over the threshold frequency? • More ejected electrons. • What happens if you increase the frequency of light if you are over the threshold frequency? • Higher kinetic energy per electron. (i.e. they move _____________)
Wave Interference: Clearing up a misconception Constructive • Waves with same phase interfere constructively • They add • Waves with different phase interfere deconstructively • They subtract Destructive
Questions: • What would the pattern of light look like if light were a particle? • No interference patterns, two bright areas directly across from each hole, slowly dimming to nothing. • What phenomena is responsible for the patterns of light, what do scientist call these? • Constructive and destructive interference form the bright and dim patterns that we call “interference” patterns, where the bright bands correspond to constructive interference and the dim bands correspond to destructive interference.
Wave or Particle? • Summary: Experiments show it has properties of both. • Photo electric effect: • Particle like • Double split experiment • wavelike • This is true of very small matter as well as light • Largest so far to have measurable wave-like properties is those with mass 1610 amu
Light vs. Small Matter vs “Big” matter Light: no mass, wave particle duality Small matter: Has mass wave particle duality Wavelength is same or larger order of magnitude as size Large matter: Has mass No appreciable wave particle duality (you can still calculate it, but it doesn’t affect our interactions with it and you can’t measure it.) Wavelength much less than size
How did we get to the pictures of orbitals we have now…. Schrodinger equation solutions Multi electron atoms= many types of approximation, no exact solutions Particle in a box (1d) Particle in a box (2/3D) Hydrogen Atom Subject of Current research: We saw result, of appoximations Didn’t cover
Sign Conventions for Energy: *common error causes* ΔE is + • A free electron has ΔE=0 • Energy levels are negative, most negative and therefore lowest energy is n=1 • ΔE is positive if going from low to high energy shell i.e. ground state to anything, 25 ect… Words such as “photon absorbed” will be used. • ΔE is negative if going from high to low energy. i.e. anything to ground state, 52 ect… Words such as “photon emitted” will be used. • E=hν=hc/λ This energy is the energy of one photon. This must always be positive! ΔE is -
Emission vs. absorption vs reflection Emission: light is “created” (not strictly scientific wording there) by the change in energy of electrons. Absorption: light is taken into an object and either raises the energy level of an electron or is converted to heat Reflection: light “bounces off” object
Quantum numbers What is the quantum numbers for the highest energy electrons in phosphorous? n=4, l=> p orbital so l=1 How many orbitals and electrons are in the n=3 and n=2 energy levels. n=3 l= 0, 1, 2 ml=0; -1,0,1; -2, -1, 0, 1, 2=9 orbitals n=2 l= 0, 1 ml=0; -1,0,1=4 orbitals 9+4=13 orbitals 2 electrons= 13*2=26 electrons
Shielding and Penetration • Orbitals with radial probability closer to the nucleus are more penetrating. • The closer, more penetrating orbitals, are shielding the further orbitals from the nucleus. • What is the electron configuration of the Fe atom? Which orbital is most shielded? • [Ar]4s23d6