Exam 2 Practice Problems (Key) 1. An electron has an n value of 3. What are the possible l values? What are the possible m l values?

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1 Exam 2 Practice Problems (Key) 1. An electron has an n value of 3. What are the possible l values? What are the possible m l values? l = 0, 1, 2 m l = 0 (for s) m l = 1, 0, +1 (for p) m l = 2, 1, 0, +1, +2 (for d) 2. Below is the electron energy diagram for hydrogen in the ground state. Draw the electron energy diagram of helium in the ground state relative to that of hydrogen shown below. Energy 1s 1s 3. In lecture we discussed how the Bohr equation could be used for any oneelectron system. a. What is meant by a oneelectron system? Any atom or ion with only one electron. b. List three oneelectron systems., e +, Li 2+, c. What is the energy of an electron in n = 4 of e +?! E = 2.179x10 18 J 2 2 $ # &= x10 19 J = 5.448x10 19 J " 4 2 % d. What is the energy of an electron in n = of e +? " E = 2.179x10 18 J 2 2 % $ '= 0 J # 2 & e. ow much energy is needed to remove an electron from n = 4 of a e + ion? 5.448x10 19 J

2 f. What is the frequency and wavelength of light describes in part e? E=hυ υ= E h = 5.448x10 19 J 6.626x10 34 J s = x1014 z = 8.222x10 14 z E=h c λ λ=h c E = ( 6.626x10 34 J s) 2.998x10 8 m/s 5.448x10 19 J = x10 7 m = 364.6nm 4. Write the electron configuration for S 2, l, K +, a 2+ Each of these atoms/ions has the same number of electrons, so their electron configurations will be the same; 1s 2 2s 2 2p 6 3s 2 3p 6 5. Rank sulfide, chloride, potassium ion, and calcium ion in terms of size. a 2+ < K + < l < S 2 6. Write a chemical equation with a change in energy equal to IE 2 for a nitrogen atom. N + (g) N 2+ (g) + e 7. Write a chemical equation with a change in energy equal to EA 2 for a nitrogen atom. N (g) + e 2 N (g) 8. Which element in row two of the periodic table has the following ionization energies. IE (kj/mol) The relatively large jump is from IE 8 and IE 9. This is an indication there are eight valence electrons, which would correspond to neon.

3 9. What are the four quantum numbers and what do they indicate? Principal number (n) Represents the size of the orbitals Angular momentum number (l) Represents the shape of the orbitals Magnetic number (m l ) Represents the orientation of the orbitals Spin number (m s ) Represents the spin of an electron 10. Write out the full length and condensed electron configuration for Na, S, Mo, Ne, and Dy. Sodium ull: 1s 2 2s 2 2p 6 3s 1, condensed: [Ne]3s 1 Sulfur ull: 1s 2 2s 2 2p 6 3s 2 3p 4, condensed: [Ne]3s 2 3p 4 Molybdenum ull: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 4, condensed: [Kr]5s 2 4d 4 Neon ull: 1s 2 2s 2 2p 6, condensed: [e]2s 2 2p 6 Dysprosium ull: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 10, condensed: [Xe] 6s 2 4f ow many valence electrons do each of the elements in the previous problem have? Na = 1 S = 6 Mo = 6 Ne = 8 Dy = What is the molecular geometry of I 3? I I I Molecular Geometry = Linear 13. What is the indicated bond angle in the following molecule? >120

4 14. Which of the following molecules have the same number of valence electrons as N 2? a. 2 b. N 2 c. 3 d. 3 e What is the formal charge of nitrogen in the following Lewis dot structure? N ormal harge = Draw the Lewis dot structure for I 5. I 17. Draw the Lewis structure for Xe 2 2. Xe 18. There are three possible resonance structures for N 2. Draw all three and determine which is the most reasonable. Best structure based on formal charges N N N N N N ormal charges

5 19. Draw a Lewis dot structure AND perspective drawing for S 6. S S Lewis dot structure Perspective drawing 20. Which of the following are polar molecules? ( 2, 4, 2, 3 l, 2, 2 l 2 ) Polar Non Polar Non Polar l l l Non Polar Polar Polar 21. What is the concentration of Na in a solution made by mixing 5.00 grams of solid sodium hydroxide with enough water to make a total volume of ml? 5.00 g Na ml 1000 ml mole Na x x = M Na L g Na

6 22. What is the concentration of Mgl 2 in a solution made by dissolving grams of magnesium chloride in enough water to make a final volume of ml? g Mgl ml 1000 ml x x mole Mgl 2 = M Mgl 2 L g Mgl What is the concentration of chloride ions in the solution described in the previous problem? g Mgl ml 1000 ml x x mole Mgl 2 2 mole l x = M l L g Mgl 2 mole Mgl ow much KN 3 is required to make 1.00 liters of M KN 3? 1.00L x mole KN 3 L x g KN 3 mole KN 3 = 50.6 g KN A diluted Mgl 2 solution is made by mixing ml of M Mgl 2 with ml of water. What is the concentration of the newly diluted solution? 1 V 1 = 2 V 2 ( )( ml) ( ) 2 = V 1 1 = M Mgl 2 V ml = M Mgl 2