Chem Discussion #12 Chapter 8 and 10 Your name/ TF s name: Discussion Day/Time:

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1 Chem 0 07 Discussion # Chapter 8 and 0 Your name/ TF s name: Discussion Da/Time: Things ou should know when ou leave Discussion toda for one-electron atoms: En = -R n = J n = -3.6eV ΔEmatter=En-Em ; Ionization Energ(IE)=E En(initial) ΔΕlight=hνlight= IE +KE n. 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.( next to the lines on the right ) 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 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? f. What is the ground state H atom ionization energ in J, ev and kj/mol? (H(g) H + (g) + e - ) g. What is the expression for the ionization energ of an electron from the n=3 state of an atom with atomic number?

2 . Hpothetical atom, X, has the following ground state absorption spectrum (displaed below), and the ground state ionization energ of the atom is 5eV (IE). Each of the absorption lines corresponds to a natural frequenc of the electron cloud resulting from the mixing of electron wave with loop with electron wave with more than one loop (i.e. the atom alwas starts in its ground state in 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? (Careful of a 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 did draw: How man lines will be present 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?

3 (g) Can atom X emit light of energ 3 ev? (h) Is it possible for X to absorb light of energ 6eV or will it be transparent to it? Wh? (i) Can atom X emit light of energ6 ev? (j) What is the lowest frequenc of the light emitted from the atom? (k) Draw the emission spectrum: 3. What is the expression for the energ in J for the ground state of an electron cloud in Li +? a. Calculate wavelength (in nm) of the light corresponding to the Li + electron cloud resulting from mixing a 3 loop electron wave with a loop electron wave? (Answer:nm) 4. What electron cloud energies account for the line corresponding to the wavelength 434 nm in the gas discharge spectrum for the Balmer series of H atoms? (In the Balmer series in each of the emission lines corresponds to a natural frequenc of the electron cloud resulting from the mixing of an electron wave with more than two loop with the electron wave with 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 = and n = 4 cloud energies E. The n = and n = 5 cloud energies F. None of these. 5. Photons of energ 3.6eV=R are able to ionize H in its n = energ level. Are photons of this energ are able to ionize He + in its n = energ level? 3

4 6. The light with wavelength of 365 nm will ionize H atom in the n = 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 7. The light with wavelength of 365nm will ionize H atom in the n = energ level. What effect will light with wavelength = 65nm 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 8. The photoelectric effect threshold frequenc of a metal is υ0 = 0 5 Hz. Gamma radiation of frequenc 0 7 Hz ejects electrons from the metal. Which of the following occurs when the intensit of the gamma radiation is reduced b 50 %? 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. 9. 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. 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. 0. An electron is ionized from the ground state of an atom, with E = J, b light with frequenc Hz. What is the kinetic energ (in ev) of the ejected electron? 4

5 . The work function (ionization energ), of chromium metal is 7.x0-9 J. What is the maximum kinetic energ of an electron, if it is ejected from chromium metal b light of wavelength 50.nm? a. What will happen to the speed and quantit of the ejected electrons if the wavelength of the light will increase? b. What will happen to the speed and quantit of the ejected electrons if the wavelength of the light will decrease? c. What will happen to the speed and quantit of electrons if the intensit of the light will increase?. An atom has onl three energ levels, -.5, -4.0, 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) b. Draw the emission spectrum. (Hint: does it alwas just goes to the ground state?) 3. An atom has onl three energ levels, -.6, -4., and -5 ev. Draw the absorption spectrum for a gas of these atoms excited b an electric discharge. b. List all the lines in the emission spectrum. Do not assume that it alwas goes to the ground state. 4. One atom emits light of energ.7 ev. A second atom has onl three energ levels: -0.9 ev, -.7 ev, and -.9 ev. Assuming ionization is not possible can the second atom absorb the light emitted b the first atom. 5

6 Useful information: Atomic wave function famil album a. Principle quantum number n=,,3, specifies energ level n= j+l b. Number of nodal planes (l). c. Angular momentum quantum number (l=0,,, n-) defines the shape of the orbital. d. ml= -l,.0 l e. Number of loops j (j=n-l) f. S, P and D and F orbitals. g. Size of the orbital is proportional to n Electron configuration a. Orbital, Shell, Subshell b. Shielding c. Pauli Exclusion Principle. Auf-bau. Hund s rule Periodic Trends (I.E., E.A., Radius, Ionic Radius, Electronegativit) For man electron atoms: eff 8 eff kj eff En 3.6(eV).8 0 (J) 3 n n mol n Useful Information Below 3dx, 3dx - and 3dz orbital. Be sure to correctl orient our orbitals in the x--z space. 6

7 Orbital l n=j+l j= n-l Shape Number of orbitals in a subshells(ml) l+ orientation in space s Sphere etc j=n p d 3 4 etc 3 4 etc 3 j=n- j=n- Dumbbell # e - that can fit 3 6 Cloverleaf 5 0 f etc j=n 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. 3dx). A z 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 orbitals of same n have the same energ.). What are the possible angular momentum quantum numbers for an orbital in the n=4 shell? How man degenerate orbitals are in the n=3 shell? What are the?(note: in H atom, all orbitals of same n have the same energ.) 7

8 3. 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.( Answer: 0.85) A: B: C: Additional Practice problems:. The ionization wavelength of H atom in the n = energ level is 365 nm. Will light of this wavelength ionize He + in the n = level?. An electron is ionized from the ground state of an atom, with E = 30 ev, b light for which a photon of light energ is 36 ev. What is the kinetic energ (in ev) of the ejected electron?( Answer: 6eV) 3. What is kinetic energ of the electron ionized from Li + in its n = 6 level b light of wavelength 30 nm?(answer: 0.94*0-9 ) 4. In terms of the variables ( like: 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? 5. What is the largest possible wavelength of light that will be emitted b be the Li + atom with the energ level corresponding to 6 loops?(answer: 800nm) In preparation for lectures and next week discussion: Please bring Page 9 and 0 below to the lectures until completed 8

9 Atom He Li 3 Be 4 B 5 Electron configuration IE kj mol eff Trends in IE is Explained b: a. increases b. Electron electron repulsion c. New shell d. l increases or eff decreases (shielding) Ions (Ions Electron configuration) s 373 He + s s 50 s s 899 s Li + s Be + s s 80 B + C 6 N 7 O 8 F 9 s p x p s 086 s px p pz C + s s px N + s s p x p O + s s px p pz s 680 F Ne Na s s p Mg [ Ne]3s x p p z 3s 738 Ne + p p p s s x z Na + p p p s s x z Mg + [ Ne ]3s Al 3 [ ]3s 3px Ne 578 Al + [ Ne ]3s 9

10 Atom He Ions (Ions Electron configuration) Li 3 Li + IE kj mol He + s 548 s Be 4 Be + B 5 s s B eff For the Ions Trends in IE is Explained b: a. increases b. Electron electron repulsion c. New shell d. l increases or eff decreases (shielding) C 6 C + s s px s s p x p N 7 N s s p p p O 8 O + F 9 x z F s s p p p Ne 0 Ne + x z s s p p p Na Na + x z Mg Mg + [ Ne ]3s Al 3 Al + [ Ne ]3s 0

11 6. 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? 8 a. Calculate eff of C, if IE = 086 kj/mol.(hint: IE= E -E eff initial=.8 0 (J) ) n. - H(BA) + H(BE) + H(EC). a. For water, B is < than D. Exam 3 answers: b. For water, slope of A is > than slope of C. c. For water, slope of C is < than slope of E. d. B for water is > B for ammonia (NH3). e. D for methane (CH4) is < D for methanol (CH3OH). 3. a. -88 kj/mol b kj/mol c. -4 kj d. 50. kj.mol e. 6 kj/mol 4. a J b ºC 6. C6H (l) + 9O (g) 6HO( l) + 6CO( g) 7. a. -38 kj/mol b. qp < 0 w > 0 ΔU < 0 8. C<C3<C 9. F, F, F, T, F Hz. 74.5% Tfinal (constant pressure) > Tfinal (constant volume)