Photons in / Photons out 6.1.2 Energy Levels

Ionization IONIZATION ENERGIES Energy needed to liberate electron from that level. GROUND STATE Lowest possible energy state for an electron in an atom.

Use the energy level diagram Example #1 A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron. What minimum energy did this photon have? Try it! Use the energy level diagram

So the photon had to provide to ionize/liberate the electron Example #1 A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron. What minimum energy did this photon have? Free/liberated electron energy So the photon had to provide 13.6 eV to ionize/liberate the electron Ground state energy (in eV)

Example #1 A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron. What is the frequency of the photon that could provide this energy? We have energy and need to find frequency… We can use our equation E=hf!! BUT… our energy is in eV, not joules First convert the ionization energy from eV into J

Example #1 A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron. What is the frequency of the photon that could provide this energy? Conversion table!

Example #1 A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron. What is the frequency of the photon that could provide this energy? Value to convert Conversion factor (p.1 of Ref table) 1 eV = 1.6 x 10-19 J 1 eV 1.6 x 10-19 J 13.6 eV

Example #1 A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron. What is the frequency of the photon that could provide this energy? Value to convert Conversion factor (p.1 of Ref table) 1 eV = 1.6 x 10-19 J 1 eV 1.6 x 10-19 J 13.6 eV = 2.18 x 10-18 J

Example #1 A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron. What is the frequency of the photon that could provide this energy? Now that we have energy of the photon in Joules, we can use an equation to solve for the frequency of this photon (Yesterday’s lesson!)

Example #1 A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron. What is the frequency of the photon that could provide this energy? Ephoton = 2.18 x 10-18 J f = ? h = 6.63 x 10-34 J·s Ephoton = hf = hc/λ Ephoton = hf f = (2.18 x 10-18 J )/ (6.63 x 10-34 J·s) f = 3.29 x 1015 Hz

Back to our old friend, the energy level diagram for hydrogen… Example #2 What happens to an electron in the n = 2 state of a hydrogen atom if it is hit by a 5.4 electron-volt photon? Back to our old friend, the energy level diagram for hydrogen…

Energy for this electron = Example #2 What happens to an electron in the n = 2 state of a hydrogen atom if it is hit by a 5.4 electron-volt photon? State of n=2 Energy for this electron = -3.4 eV

Example #2 What happens to an electron in the n = 2 state of a hydrogen atom if it is hit by a 5.4 electron-volt photon? Hype!!! Photon with 5.4 eV of energy The electron GAINS this energy and gets hype

Electron be like “peace, I’m out” with 2.0 eV of energy in it’s pocket Example #2 What happens to an electron in the n = 2 state of a hydrogen atom if it is hit by a 5.4 electron-volt photon? If the electron initially has -3.4 eV and gains 5.4 eV from the photon… - 3.4 eV + 5.4 eV = + 2 eV Electron be like “peace, I’m out” with 2.0 eV of energy in it’s pocket More scientifically… The electron will leave the atom with a kinetic energy of 2.0 eV.

Level Jumps Initial Energy level of Electron Initial Energy level of Electron Equation Energy of photon absorbed/emitted An electron will jump to a higher level if the ABSORBED photon has exactly the right energy. When an electron drops to a lower level a photon is EMITTED

Absorbing Photons Hype!!! Photon Let’s say my dude Ellie the electron is chillin in energy level n = 3. Then, Princess the photon rolls by and says “what’s up boiii” Ellie the electron absorbs princess (electrons are selfish) Ellie gets hype and gains energy! Ellie could hop to higher energy levels OR get ionized.

Emitting Photons Let’s say my dude Ellie the electron is chillin in energy level n = 5. He’s pretty hype Photon However, his girl Princess the photon decides to leave him. At the same instant, he gets sad, looses energy, and drops down to a lower energy level

Example #3 What energy is needed to move an electron from the ground state of a hydrogen atom to its n = 4 level? TRY IT

Example #3 Ephoton = Ei – Ef Ephoton = -13.6 eV – -0.85 eV What energy is needed to move an electron from the ground state of a hydrogen atom to its n = 4 level? Ephoton = Ei – Ef Ephoton = -13.6 eV – -0.85 eV Ephoton = -12.75 eV Ef Ei

Example #4 An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom. What is the energy of the emitted photon? Ephoton = Ei – Ef Ephoton = -0.85 eV – -1.51 eV Ephoton = +0.66 eV Ei Ef

Example #4 An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom. What is the frequency of this photon?

Example #4 An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom. What is the frequency of this photon? Ephoton = 1.056 x 10-19 J f = ? h = 6.63 x 10-34 J·s Ephoton = hf = hc/λ Ephoton = hf f = (1.056 x 10-19 J )/ (6.63 x 10-34 J·s) f = 1.6 x 1014 Hz

Example #5 When electrons drop from one energy level to another they can follow any path to the lower state. Each downward step produces a photon with a different energy. How many different photons could be produced in a transition from the n = 4 level of hydrogen to the n = 1 level? How many different photons could be produced in a transition from the d-level to the b-level of a mercury atom? n =4 n = 3 n = 2 n = 1 6 possible photons d c b 3 possible photons

Absorption/Emission Spectrum An EMISSION SPECTRUM is a pattern of bright lines on a dark background. Analyze glow of a heated sample An ABSORPTION SPECTRUM is a pattern of dark bands on a continuous spectrum. Pass white light through a cold sample.

Absorption/Emission Spectrum The existence of spectrums demonstrates that: Energy in atoms is QUANATIZED – comes in discrete jumps. Atoms can produce only specific sets of PHOTONS.

End of 6.1.2