Chapter 6: Electronic Structure of AtomsPages 207-247

Brief Explanation of the ChapterExplore Quantum TheoryNature of LightArrangement of electrons in atomsExploration of reactivityHistory

Wave Nature of LightKnowledge of electrons come from lightHow can we numerically define the speed of light?3.00 x 108 m/sHow do we explain the term periodic in reference to waves?Define WavelengthDefine Frequency

Wavelength of LightHow are the wavelength and frequency of electromagnetic radiation related?Why do different types of electromagnetic radiation have different properties?How do the wavelength and frequency of an X-ray compare with those of the red light from a neon sign?How do we express frequency?

PracticeHow did you determine which of the waves represented blue, and which represented red?

PracticeA laser used in eye surgery to fuse detached retinas produces radiation with a wavelength of 640.0 nm. Calculate the frequency of this radiation.An FM radio station broadcasts electromagnetic radiation at a frequency of 103.4 MHz. Calculate the wavelength of this radiation?

Quantized Energy and PhotonsWave model of light does not explain three very important phenomena.The emission of light from hot objects (blackbody radiation) The emission of electrons from metal surfaces on which light shines (photoelectric effect)The emission of light from electronically excited gas atoms (emission spectra)

Hot Objects and Quantization of Energy (blackbody radiation)1900- Max PlanckAssumed energy either released or absorbed by atoms in chunks of some minimum size.termed QUANTUM (fixed amount) to smallest quantity of energy that can be emitted or absorbedProposed that energy (E) of a single quantum equals constant times the frequency of radiationE=hv

Plancks Constanth= 6.626 x 10-34 joule-second (J-s)

Can be emitted or absorbed in whole number multiples of hv (hv, 2hv, 3hv)

If 3hv has been released, we say: 3 quanta of energy have been emitted

Stairs Vs. Ramp

Photoelectric Effect and PhotonsAlbert EinsteinLight shining on a clean metal surface causes surface to emit electronsMinimum frequency of light (different for different metals) is required for emission.Light with frequency of 4.60 x 1014 s-1 or greater causes cesium metal to emit electrons.Radiant energy striking surfaces behaves like stream of energy particles (PHOTONS)Does light act more like a wave or a particle?

Practice ProblemsA laser emits light that a frequency of 4.69 x 10^14/s. What is the energy of one photon of this radiation?If the laser emits a pulse containing 5.0 x 10^17 photons of this radiation, what is the total energy of that pulse?If the laser emits 1.3 x 10^-2 J of energy during a pulse, how many photons are emitted?

Bohr and Line SpectraNeils Bohr (1913)Theoretical explanation of line spectra

Line SpectraContinuous Vs. Line Spectra, how do they differ?

How do we produce a bright line spectra?

How is that energy emitted?

We know there is a definite change in energy, this corresponds to:Definite FrequencyDefinite Wavelength

Bohrs ModelAssumed electrons move in circular orbits around nucleusGoes against physics!! Charged particle moving in circular orbit should continually lose energy and spiral into positively charged nucleusBased model on 3 postulates:Only orbits of certain radii (with specific energies) permitted for electrons in H atom.Electron in permitted orbit is in allowed energy state and therefore does not radiate energyEnergy is emitted or absorbed as a photon only when moving energy levels

Energy States of Hydrogen AtomBohr began calculating possible energy levels and found they fit into a specific equation.

December 13th, 2012Do Now:1.Einsteins 1905 paper on the photoelectric effect was the first important application of Plancks quantum hypothesis. Describe his original hypothesis, and explain how Einstein made use of it in his theory of the photoelectric effect.2. A laser emits a wavelength of 987 nm. In what portion of the spectrum is this found? Its output energy is absorbed in a detector that measures a total energy of 0.52 J over 32 seconds. How many photons per second are being emitted?

Energy States of a Hydrogen AtomWith three postulates and classical equations for motion and interacting charges, Bohr calculated energy corresponding to orbits.

E= (-hcRH) (1/n2) = (-2.18 x 10-18 J) (1/n2)

h= plancks constantc= speed of lightRH= Rydbergs Constantn= principal quantum number (range from 1- infinity)

Energy of Hydrogen cont.Each orbit = different n valueEnergies of electrons of a H atom given by this equation are negative for all values of n (most negative being closest to 1)Lower the energy, more stable the atomLowest energy state = ground stateWhen in higher = excited state

Yikes!How is the radius effected as n becomes infinitely larger?How is the energy effected as n becomes infinitely larger? The state in which the electron is removed from the nucleus is the reference, or zero energy, state.E = Ef Ei = Ephoton = hv

Hydrogen Atom Cont.Bohrs model states that specific frequencies of light satisfy the previous equation. Therefor we can state:If nf is smaller than ni, the electron is moving closer to the nucleus and change in energy is negative *indicates a release of energy*This equation can be used to calculate frequency or wavelength as well.

Limitations to BohrBohr model can not explain line spectra beyond the Hydrogen atom (except in crude manner)As we have seen, electrons also have wavelike propertiesThings kept from Bohr Model:Electrons exist in certain discrete energy levels described by quantum numbersEnergy is involved in moving an electron from one level to another

Wave Behavior of MatterLouis de Broglie:Studied Dual Nature of Particles (wave and radiant energy)Suggested that the electron is associated with a particular wavelength. Wavelength of electron is dependent upon mass and velocity ( m and v) = h/ mvQuantity mv = momentumTermed matter waves to describe wave characteristics of particles

Practice ProblemCalculate the velocity of a neutron whose de Broglie wavelength is 500 pm. The mass of a neutron is 1.67492716 x 10-24 g.