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City College, Chemistry Department Chemistry 10301, sections E*, Prof. T. Lazaridis Third Midterm exam, Nov. 24, 2010 Last Name: _____________________________________________ First Name: _____________________________________________ SSN last 4: ______________________________________________ Note: There are 7 questions in this exam. Fill in your answer in the blank space provided immediately following each question. 1/2 point will be subtracted every time you report a numerical result with an incorrect number of significant figures. Speed of light : 2.9979 X 108 m/s Planck's constant : 6.626 X 10-34 Js 1 amu = 1.66 x 10-24 g En = -2.179 X 10-18 J/n2 Useful data: 1. (18) (a) (8) Write next to the following sets of quantum numbers whether they are permissible or not (yes or no). i) n=2 l=1 ml=1 YES ii) n=1 l=0 ml =-1 NO iii) n= 4 l=2 ml =-2 YES iv) n=3 NO l=3 ml =0 (b) (6) What is the maximal number of electrons in an atom that can have the following quantum numbers i) n=4 l=3 ml=-3 2 ii) n=5 l=3 14 ii) n=2 ms = -1/2 4 (c) (4) What is the maximal number of electrons that can occupy each of the following subshells i) 3d 10 ii) 4s 2 2. (12) (a) (3) Arrange the following atoms in order of increasing atomic radius: F, P, S, As. F < S < P < As (b) (3) Based on their positions in the periodic table, circle the atom in the following pairs that will have the larger first ionization energy: K, Cr O, Ne Ge, Sn (c) (3) Based on their positions in the periodic table, circle the atom in the following pairs that will have the greater metallic character: Li, Be Sn, P Al, B (d) (3) The electron affinity for Br is +325 kJ/mol and for Kr -39 kJ/mol. Explain this difference in terms of the electron configuration of the two elements. Br has s2p5 and Kr s2p6 configuration. It is favorable for Br to gain one more electron to complete the octet. For Kr the extra electron would have to go to the 5s orbital and the attraction would the nucleus would be small compared to the electron-electron repulsion, hence electron abstraction is unfavorable. 3. (10) (a) (5) Which radiation has higher energy: radiation from an x-ray machine, the signal used in radio broadcasting, or light from an orange-red neon light? x-rays (b) (5) What is the frequency of radiation that has a wavelength of 0.589 pm? v= c/λ = 2.9979 X 108m/s / 0.589 X 10-12 m = 5.09 X 1020 sec-1 4. (10) What is the wavelength of a lithium atom moving at 6.5 X 105 m/s? mass = 6.941 amu = 6.941 * 1.66X10-24 g λ = h/mυ = 6.626 X 10-34 Js / 6.941 * 1.66X10-27 Kg * 6.5 X 105 m/s = 8.8 X 10-14 m 5. (10) Calculate the frequency, energy, and wavelength in nm of the radiation corresponding to a transition of an electron from n=5 to n=1 in the H atom. In what area of the electromagnetic spectrum does this radiation fall? 2.179X10-18(1/1 – 1/52) = 2.092X19-18 J (the energy) energy = hv => v= 2.092X19-18 J / 6.626 X 10-34 Js = 3.157 X 1015 sec-1 λ = c/v = 9.496 X 10-8 m = 94.96 nm (ultraviolet) 6. (25) Give the electron configuration and the orbital diagram (valence electrons only) of the following elements or ions (use noble gas core abbreviated notation): a) (5) Sc [Ar] 4s2 3d1 3d 4s b) (5) Fe3+ [Ar] 3d5 3d [Kr] 5s2 4d105p5 c) (5) I 5p 5s d) (5) Se2- [Kr] 4s e) (5) Sn2+ 4p [Kr] 5s2 4d10 5s 7. (15) Use data from the tables of ionization energies and electron affinities to determine whether the following reaction is endothermic or exothermic and the enthalpy of the reaction: Mg (g) + 2 Cl (g) Mg2+ (g) + 2 Cl- (g) Mg (g) Mg+ (g) + e- ΔH = +738 kJ Mg+ (g) Mg2+ + e- ΔH = +1451 kJ Cl + e- Cl- ΔH = -349 kJ Multiply last by two and add to first two: 738 + 1451 -2 * 349 = +1491 kJ (endothermic)