CH 101Fall 2018 Discussion #12 Chapter 8, Mahaffy, 2e sections Your name: TF s name: Discussion Day/Time:

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1 CH 11Fall 218 Discussion #12 Chapter 8, Mahaff, 2e sections Your name: TF s name: Discussion Da/Time: Things ou should know when ou leave Discussion toda for one-electron atoms: ΔE matter=e n-e m ; Ionization Energ(IE)=E E n(initial) ΔΕ light = hν light = IE + KE e 1. Consider the following energ levels of the hdrogen atom as shown below in the diagram: a. Sketch electron clouds corresponding to energ levels up to n = 3: f. What is the ground state H atom ionization energ in J, ev and kj/mol? H(g) H + (g) + e - b. When electron cloud of the H atom at the lowest energ interacts with light of the lowest resonate frequenc, sketch the resulting electron cloud(s): c. When electron cloud of the H atom at the lowest energ interacts with light of the 2 nd lowest resonate frequenc, sketch the resulting electron cloud(s): d. When electron cloud of the He atom at the lowest energ interacts with light of the lowest resonate frequenc, sketch the resulting electron cloud(s): e. What are the two energ levels involved in the ionization energ of an electron from H in the ground state? g. What is the expression for the ionization energ of an electron from the n = 3 state of a one electron atom with atomic number Z?

2 2. Hpothetical atom, X, has the following ground state absorption spectrum displaed below, and the ground state ionization energ of the atom is 15 ev (IE). Each of the absorption lines corresponds to a natural frequenc of the electron cloud resulting from the mixing of electron wave with 1 loop with electron wave with more than one loop (i.e. the atom alwas starts in its ground state during each absorption). In answering the following questions, assume that the zero of energ is the ionized atom X X + + e - a. What is the energ of the ground state (of the electron cloud corresponding to one loop) of X? Hint: pa attention to the sign b. Construct the energ level diagram for X. Hint: How man energ levels are necessar to account for the absorption spectrum? c. Using the energ level diagram ou just drew: How man emissions are possible in the electricall-excited emission spectrum of this atom? d. What is the energ of the third excited state of X? How man loops does that state have? e. What is the energ of the highest energ state of X that is necessar to account for the absorption spectrum? f. Is it possible for an electron in the ground state of atom X to absorb light of energ 3 ev or will it be transparent to it? 2

3 g. Can atom X emit light of energ 3 ev? h. Is it possible for X to absorb light of energ 16 ev or will it be transparent to it? Wh? i. Can atom X emit light of energ16 ev? j. What is the lowest frequenc of the light emitted from the atom? k. Draw the emission spectrum: l. At home: Calculate the kinetic energ of an electron (in Joules) that was ionized b light of frequenc of Hz from the ground state. Hint: Remember that energ must be conserved. ( J = 1 ev) 3. What is the expression for the energ (in J) for the ground state of an electron cloud in Li 2+? a. Calculate wavelength (in nm) of the light corresponding to the Li 2+ electron cloud resulting from mixing a 3 loop electron wave with a 1 loop electron wave? 4. Photons of energ 13.6 ev = R are able to ionize H in its n = 1 energ level. Are photons of this energ are able to ionize He + in its n = 2 energ level? 5. The photoelectric effect threshold frequenc of a metal is υ = Hz. Gamma radiation of frequenc Hz ejects electrons from the metal. Which of the following occurs when the intensit of the gamma radiation is reduced b 5.%? a. The velocit of the ejected electrons will be reduced b a factor of two. b. The kinetic energ of the ejected electrons will be reduced b a factor of two. c. The kinetic energ of the ejected electrons will be reduced b a factor of four. d. Kinetic energ and the velocit of the ejected electrons will sta the same. e. Number of ejected electrons will increase. f. Number of ejected electrons will decrease. 6. Assume light is able to eject electrons from a metal. What do ou expect as the wavelength of the light is increased? a. If the light wavelength reaches the lowest, electrons will no longer be ejected. 3

4 b. Electrons will still be ejected but the will move faster and faster. c. Electrons will still be ejected but the will move slower and slower. d. More and more electrons will be ejected but the will have the same kinetic energ. e. More information needed. 7. One atom emits light of energ 1.27 ev. A second atom has onl three energ levels: -.9 ev, ev, and -1.9 ev. Assuming ionization is not possible can the second atom absorb the light emitted b the first atom. 8. For the two hdrogen electron clouds below identif the quantum number n, the quantum number l, the number of radial loops j, and the specific name of the orbital ou must indicate orientation, e.g. 3d x). A z B n = l = j = n = l = j = z x x name: name: a. For the two hdrogen electron clouds above, which has the largest ionization energ? Note: in H atom, all orbital of the same n have the same energ. 9. What are the possible angular momentum quantum numbers for an orbital in the n=4 shell? a. How man degenerate orbitals are in the n=3 shell? What are the? Note: in H atom, all orbitals of the same n have the same energ. 1. The figure shows three H atom electron clouds. a. Which of the following H atom electron clouds has the largest ionization energ? b. Write down the numerical expression that when evaluated gives the value in ev of smallest ionization energ of these three clouds. A B C Things ou should know when ou leave Discussion toda for multi-electron atoms: Man electron sstem Mahaff, 2e section 8.4 Electron configurations Mahaff, 2e section 8.5 4

5 Ionization Energ (MJ/mol) Shielding and effective nuclear charge: Mahaff, 2e section 8.6 o Periodicit: Mahaff, 2e section 8.7 e 1. Below is a plot of the first 1 ionization energies for a single atom in 3 rd row of the periodic table. The x-axis shows which ionization (e.g. IE 1, IE 2, etc.) and the -axis gives how much energ in (MJ/mol). a. What 3 rd row element does the plot show? b. First ionization energ IE 1 is 1.36 ev calculate Z eff for that element. Note: We will not use Slater s rules for eff, so please ignore Mahaff et al., section 8.6, pages 289 to 291.(Useful information: 1eV = J; A = /mol) IE= E - E initial= = e c. The arrow points to the jump between the 6 th and 7 th ionization energ. Which of the following statements are true? i. The number of protons (Z) changed. ii. The effective nuclear charge (Z eff) changed. iii. The quantum number n of the electron that is ionized changed. iv. The radius of the ion decreased # of Electrons Ionized 2. From the following three different neutral atoms electron configurations, label the one with the highest third ionization energ, and lowest third ionization energ. Explain our 5

6 answers. Hint: remember that number of electrons in the neutral atom equals the number of protons. a. 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 b. 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 c.1s 2 2s 2 2p 6 3s 2 3p 6 3. Which one will have the greatest ionization energ: Na +, Ne, F -, O 2-? 4. Answer the following questions about manganese (Mn): a. What is the electron configuration? b. First ionization energ IE 1 is 7.43 ev calculate Z eff for that element. c. Circle the letters corresponding to the picture of occupied electron clouds. Hint: ou need to know what are n, l, and j for one electron in each of the occupied electron clouds. A B C D E F For the G H I pictures above, fill in the empt boxes on the graphs on the next page with corresponding names of the orbitals (1s, 2s, 3s, 4s, 2p, 3p, 3d): 6

7 Probabilit Probabilit Probabilit Probabilit Probabilit Probabilit Probabilit d. Use the radial probabilit densities on the next page (electron cloud cross section below) to estimate the size of an atom of Mn. Hint: Look at the x axis Distance from Nucleus (Angstroms) Distance from Nucleus (Angstroms) Distance from Nucleus (Angstroms) Distance from Nucleus (Angstroms) Distance from Nucleus (Angstroms) Distance from Nucleus (Angstroms) Additional Practice Problems What electron.1 cloud energies account for the line.8 corresponding to the wavelength 434 nm in the gas discharge.6 spectrum for the Balmer series of H atoms? (In the.4 Balmer series in each of the emission.2 lines corresponds to a natural frequenc of the electron cloud resulting from the mixing of an electron wave Distance from Nucleus (Angstroms) with more than two loop with the electron wave with 2 7

8 loop) A. Onl the n = 3 cloud energ B. Onl the n = 4 cloud energ C. Onl the n = 5 cloud energ D. The n = 2 and n = 4 cloud energies E. The n = 2 and n = 5 cloud energies F. None of these. 2. The ionization wavelength of H atom in the n = 2 energ level is 365 nm. Will light of this wavelength ionize He + in the n = 1 level? 3. The light with wavelength of 365 nm will ionize H atom in the n = 2 energ level. What effect will light with wavelength 657 nm have? (Choose all that appl.) a. Atom will be transparent to the light of this wavelength b. Ionization will take place c. Ionization will not take place d. The ionized electron will use excess energ for kinetic energ 4. The light with wavelength of 365 nm will ionize H atom in the n = 2 energ level. What effect will light with wavelength 265 nm have? (Choose all that appl.) a. Atom will be transparent to the light of this wavelength b. Ionization will take place c. Ionization will not take place d. The ionized electron will use excess energ for kinetic energ 5. An electron is ionized from the ground state of an atom, with E 1 = 3 ev, b light for which a photon of light energ is 36 ev. What is the kinetic energ (in ev) of the ejected electron? 6. What is kinetic energ of the electron ionized from Li 2+ in its n = 6 level b light of wavelength 31 nm? 7. In terms of the variables (i.e. R, h, and c) what is the smallest possible wavelength of light that will be emitted b a He + atom starting with the energ corresponding to 6 loops? 8. What is the largest possible wavelength of light that will be emitted b be the Li 2+ atom with the energ level corresponding to 6 loops. 9. An electron is ionized from the ground state of an atom, with E 1 = J, b light with frequenc Hz. What is the kinetic energ (in ev) of the ejected electron? 1. The work function ionization energ, of chromium metal is -19 J. a. What is the maximum kinetic energ of an electron, if it is ejected from chromium metal b light of wavelength 25. nm? b. What will happen to the speed and quantit of the ejected electrons if the wavelength of the light will increase? c. What will happen to the speed and quantit of the ejected electrons if the wavelength of the light will decrease? 8

9 d. What will happen to the speed and quantit of electrons if the intensit of the light will increase? 11. An atom has onl three energ levels, -2.5, -4., and -4.5 ev. Draw the absorption spectrum for a gas of these atoms excited b an electric discharge. Hint: ou need to draw energ level diagrams to answer this question assume the most negative energ is an energ of the ground state a. Draw the emission spectrum. Hint: does it alwas just go to the ground state? 12. An atom has onl three energ levels, -2.6, -4.1, and -5 ev. Draw the absorption spectrum for a gas of these atoms excited b an electric discharge. a. List all the lines in the emission spectrum. Do not assume that it alwas goes to the ground state. 13. An atom has energ levels of J, J, J, J, J, and J. a. Calculate the λ in nm of light that is necessar to excite an electron to E from E 2. b. What is the λ in nm of light necessar to excite an electron to E 3 from E 2? c. How man emission lines (in total) are possible for an atom with these energ levels? d. How man ground-state absorption lines are possible for an atom with these energ levels? 14. Draw the electron configuration diagram for C, but fill the diagram as if the C is in the ground state. Draw a dotted line around a shell. Circle a subshell. Draw a triangle around an orbital. Is C atom paramagnetic or diamagnetic? a. Calculate Z eff of C, if IE 1 = 186 kj/mol. (Hint: IE= E -E initial ) 15. Rank the following in terms of increasing ionization energ: Na, Li, B, N, Ne 16. Rank the following in terms of increasing ionization energ: Li +, B +, N +, Ne +, Na Write the ground state electron configuration for the following atoms and ions and determine if each is paramagnetic or diamagnetic: Al, Al 3+, V, V 3+ 9

10 Atom Z Electron configuration IE 1 Z eff Trends in IE1 is explained b: a. Z increases b. Electron electron repulsion c. New shell d. l increases or Zeff decreases (shielding) Ions (Ions Electron configuration) He 2 1s He + 1s 1 Li 3 1s 2 2s 1 52 Li + 1s 2 Be 4 1s 2 2s Be + 1s 2 2s 1 B 5 81 B + C C + N 7 14 N + O O + F F + Ne 1 28 Ne + Na Na + Mg 12 = e 738 Mg + e Al 13 e 578 Al + e 1

11 Atom Z Electron configuration IE 2 Z eff Trends in IE2 is explained b: a. Z increases b. Electron electron repulsion c. New shell d. l increases or Zeff decreases (shielding) He 2 He + 1s Li 3 Li + 1s 2 73 Be 4 Be + 1s 2 2s B 5 B C 6 C N 7 N O 8 O F 9 F Ne 1 Ne Na 11 Na Mg 12 Mg e Al 13 Al e 11

12 Handout Answers: 1. ds a. n=1 n=2 n=3 b. c. d. e. n and n f. IE = -18 J = 13.6eV = 1312 g. IE = R 2. a. -15 ev b. 6 c. 15 emissions d. -8 ev, 4 loops e. -3 ev, 6 loops f. No g. Yes h. Yes i. no j. 2.4*1 14 Hz k. (1 lines) l. KE= J 3. -9R a nm 4. Yes 5. D,F 6. C 7. No 8. 4d zx, 4p a. The same 9.,1,2,3 1. 2s, 4p, 3d a. 2s b..85 (n 4 to n ) Man Electrons Atoms: 1. a. Sulfur b. ii, iii, iv 2. a highest, c lowest 3. Na + 4. a. [Ar] 4s 2 3d 5 b. All except C & F c. Left column: 1s, 4s, 2p; Right column: 2s, 3s, 3p; Bottom: 3d d. Å Additional Practice Problems: 1. E 2. No 3. A, c 4. B, D 5. 6eV 6..94*1-19 J 7. =9hc/35R 1hc 8. 11R eV 1. a J b. Speed decreases, number will still the same c. Speed increases, number of electrons will sta the same d. Speed stas the same, number of electrons will increas 13. a. 361 nm b. 662 nm c. 15 lines d. 5 lines 14. Z eff = Na < Li < B < N < Ne 16. B + < N + < Ne + < Na + < Li Al: 1s 2 2s 2 2p 6 3s 2 3p 1 paramagnetic Al 3+ : 1s 2 2s 2 2p 6 3s 3p diamagnetic V: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 3 paramagnetic V 3+ : 1s 2 2s 2 2p 6 3s 2 3p 6 4s 3d aramagnetic 12

13 Atom Z He 2 Li 3 Be 4 B 5 Electron configuration IE 1 kj mol Z eff Trends in IE 1 is Explained b: e. Z increases f. Electron electron repulsion g. New shell h. l increases or Z eff decreases (shielding) Ions (Ions Electron configuration) 1s a He + 1s 2 2s c, d 1s 2 2s s 2px s IE 2 kj mol 1s Li + 1s 2 a,b Be + d 1s 2 2s B C 6 N 7 O 8 F s x s s x z s s x z s s x z s a C s 2s 2p 1 x a N s 2s x 1 b O s 2s a 1 x z F Ne 1 Na s x z s s 2s x z 3s [ Ne]3s 2 2 1s 2s Mg 12 2 [ Ne]3s 2 x z 3s a,b Ne s 2s x z c, d Na s 2s 1 x z a Mg + 1 [ Ne ]3s Al [ ]3s 3px Ne d Al + 2 [ Ne ]3s

14 Exam 3 Answers: kJ 2. 12C(s, graphite) +11H 2(g) +11/2 O 2(g) C 12H 22O 11( ) 3. 6C(s, graphite) +9H 2(g) +3/2 O 2(g) CH 3CH 2OH( ) 4. Cc a kj/mol b kj/mol c kJ kj/mol kj/mol 7. a. 1.81*1-1 s b. 656nm c. -276Kj 8. < ; > ; < ; > ; (const. pressure) < (const. volume) 9. 3,4,2,2,1 3s,4d,2p 1,5,3 B C 11. J 12. F,F,T,F,F kj/mol 14