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8 Lower Frequency Higher Frequency

9 Although the wave model of light explains many aspects of the behavior of light, several observations of electromagnetic radiation are not explained by this model: 1. The emission of light from hot objects (blackbody radiation) wavelength distribution depended on temperature (red is cooler than yellow) 2. Photoelectric effect emission of electrons from metal surfaces on which light shines 3. Emission spectra emission of light from electronically excited gas atoms.

10 He called this fixed amount a quantum the smallest amount of energy than can be emitted or absorbed as electromagnetic radiation.

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13 Plank proposed that the energy, E, of a single quantum equals a constant time the frequency of the radiation.

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19 Summary Electrons do not eject un.l the threshold frequency is reached, even a7er prolonged exposure. (1- to- 1 rela/onship of electron to another par/cle related to energy) Once the threshold frequency is reached, ejec.ons take place immediately.(further supports 1- to- 1 idea because energy is not slowly absorbed) At a set frequency, the velocity of all ejec.ons is the same; however, increasing frequency increases velocity of ejec.ons. (frequencies have different energy levels) For there to be 1- to- 1 rela.onship, energy must be in par.cles (now known as photons)

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21 So this equation can be used to determine energy per photon or frequency. Doing so provides proof that photons in high frequency light (violet) contain more energy than photons in low frequency light (red).

22 When Rutherford discovered atomic nuclei, Niels Bohr proposed that the electrons moved around the nucleus in orbits of specific radii with specific energies. The only way the electron could move from that orbit would be to emit or absorb energy as a photon with a specific quantum of energy. i.e. Ground state vs excited state and the emitted line spectrum. He created a formula to calculate the energy, but it only worked for hydrogen, not atoms with multiple electrons.

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24 So why wouldn t Bohr s calcula/ons work with mul/- electron atoms?

25 Coulomb s Law hgps:// v=ryjo774uphi

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28 Watch youtube video on shielding effect: hgps:// v=phkcjo- 94pQ

29 Ioniza/on Energy The minimum energy required to remove an electron from the ground state of an atom or ion.

30 Ionization energies for a given element increase as successive electrons are removed. I 1 < I 2 < I 3

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35 Based on ionization data which suggests that electrons are arranged in shells. It takes less energy to remove e - from n=2 than from n=1. Data showed n=2 can hold 8 e - and n=3 can hold a total of 18 e -.

36 The shell model offers at least one explanation for differences in ionization energies between energy levels.

37 Photoelectron Spectroscopy Watch hgps://

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39 PES data offers more detail about the energy levels. Although the 2 nd energy level can hold 8 e - not all of the ionization energies are the same as electrons are removed. This data suggests subshells exist within energy levels.

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42 Draw a photoelectron spectrum for magnesium, which includes all of the peaks but does not include exact ioniza/on energies.

43 Draw a photoelectron spectrum for potassium, which includes all of the peaks but does not include exact ioniza/on energies.

44 Consider the energy require to remove several electrons in succession from aluminum in the gaseous state. Equation for ionization Ionization Energy Al(g)! Al + (g) + e - I 1 = 580 kj/mol Al + (g)! Al 2+ (g) + e - I 2 = 1815 kj/mol Al 2+ (g)! Al 3+ (g) + e - I 3 = 2740 kj/mol Al 3+ (g)! Al 4+ (g) + e - I 4 = 11,600 kj/mol Why the jump in IE between I 1 and I 2? Why the considerably larger jump between I 3 and I 4?

45 In a step-wise ionization process, it is always the highest-energy electron (one bound least tightly in highest energy level n) that is removed first. I 1 is the first ionization energy required to remove this highest-energy electron. As more electrons are removed from an ion, the ionization energies will increase due to Coulomb s Law and the shielding effect on those lower-energy electrons (those bound more tightly), especially the core electrons.

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