121H Chemistry Fall, 2005 Name Cumulative Final Exam 170 points total Please sign the following statement: I swear that I did not cheat on this exam.
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Electronegativities: F = 4.0; O = 3.5; N = 3.0; Cl = 3.0; Br = 2.8; C = 2.5; S = 2.5; I = 2.5; H = 2.1; P = 2.1. Constants: h = 6.626 10-34 Js; c = 2.998 108 m/s; NA = 6.023 1023 mole-1; k = 1.38054 10-23 J/K R(Rydberg) = 1.097 107 m-1; R(gas) = 0.082057 Latm /moleK = 8.3145 J/moleK; 1 eV = 1.6019 10-19 J. Equations: E = h; c = ; En = -Rhc/n2; E = + T; = h/mv; x (m v) h / 2 ; Ee- = E; ln P = -Hvap/RT + C; PV = nRT; [P + a(n/V)2](V - nb) = nRT; KE = 3RT / 2 . Directions: you have two hours to do this exam. There are 20 questions, each worth 10 points, you must complete 17 of them. Scoring a total of 170 points will be considered achieving a 100%. Before turning in your exam paper, cross out the three questions you do not want to count toward your grade. Atomic and Ionic Electron Configurations Complete the valence electron configuration diagrams for each atom below and circle the electrons that would leave if each of these atoms were made into a cation with +2 charge. 1. K: 4s ___ 3d ___ ___ ___ ___ ___ Ca: 4s ___ 3d ___ ___ ___ ___ ___ Sc: 4s ___ 3d ___ ___ ___ ___ ___ a. Which atom would be least likely to form a cation with charge of +2? ____ b. For each cation, state whether it is diamagnetic or paramagnetic: K2+ c. 2. Ca2+ Which (2+) cation has the smallest ionic radius? Sc2+
Mass Defect and Isotopes Calculate the mass defect of 21Ne using the following masses (all in amu): proton mass = 1.0072764669, neutron mass = 1.0086649158, electron mass = 0.000548579911 and mass of one atom of 21Ne = 20.99395. a. b. amu Mass defect for 21Ne = Ne represents only 0.27% of any natural sample, and so contributes virtually nothing to the average atomic mass. The other two isotopes have abundances of approximately 90% and 10%, respectively. What might be their (integer) mass numbers? This cannot be solved rigorously; you need to make a good guess. Most abundant isotope (90%): ________ Less abundant isotope (10%): _________
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Nuclear Chemistry and Radioactivity The compound BN has properties remarkably similar to those of carbon, even having forms like the familiar carbon allotropes, e.g., diamond, graphite, and nanotubes. Suppose you had BN in its analog of the diamond allotrope of carbon. What 2 separate nuclear decay reactions would be required to convert the BN crystal into an actual diamond crystal? Write them out, assuming BN is entirely 12B12N. Answer: Each 12B atom would have to undergo _______ decay, by the following process: Each 12N atom would have to undergo _______ decay, by the following process:
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Gas Law and Stoichiometry Five compounds are in the family of sulfur-fluorine compounds with the general formula SxFy. If you place 0.0955 g of the compound in a 89.0 mL flask at 45.0 C, the pressure of the gas is 83.8 mm of Hg. a. How many moles of SxFy are present? b. What is the molecular weight of SxFy? c. What is the molecular formula of SxFy?
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Periodic Trends a. Place the following atoms/ions in order of decreasing size: Ca2+, Cl-, K+, S2____ > ____ > ____ > ____ Smaller atoms tend to have: ______________________ first ionization energies ______________________ electron affinities Consider the compounds LiF, RbI, KBr, and NaCl. Order them from most negative (on the left) to least negative (on the right) energy of ion pair formation. < < < Orbital Hybridization and VSEPR Theory For each molecule, indicate the hybridization used by the indicated atom, the expected valence bond angles taking into account any deviations from the ideal structures, and the name of the molecular geometry. Hybridization Valence angle(s) Molecular Geometry a. N in NO3b. Br in BrF5 c. S in S8 rings (see board) d. S in SF4 b.
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Lewis Dot Structures Draw the Lewis electron dot structure for either one of the molecules or ions below. Indicate the formal charge on each atom once you are finished. (Elvis says theres a hint below, so read that first.) AsOF3 IO2F27.
The rules for drawing Lewis structures in your textbook (p. 69) state that only atoms of C, N, O, and S can form multiple (double or triple) bonds. If you abandoned that requirement and allowed other atoms such as As or I to form multiple bonds, you could draw a Lewis structure with less charge separation, meeting Paulings electroneutrality principle! Its probably more representative of the real bonding than the one above. Gimme that one here:
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8. Atomic Orbitals and Nodes Pick an orbital: 3s, 3p, 3d. Circle one, and answer the following questions about it. How many nodal surfaces does it have? ___ How many nodal planes? ___ How many nodal spheres? ___ Sketch that orbital in the space to the right: Give a possible set of orbital quantum numbers for that orbital. n = _____; l = _____; ml = _____ If an electron occupied that orbital, would it ever be possible to find it actually inside the nucleus? 9. Resonance Structures One of the resonance structures for S4N4 is shown. All atoms have the appropriate number of lone pair electrons to complete their octet, but they are not shown. You dont need really them to answer this. What is the average bond order for an NS bond in this particular structure? ________ Would that bond be longer or shorter than the NS bond in NS+?
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Reactions in Aqueous Solutions For the reactions below, write balanced total and net ionic reactions for each and classify each reaction as a precipitation, acid/base or gas-forming reaction. a. Lithium carbonate and phosphoric acid Total: Net ionic: b. Lead acetate and potassium bromide Total: Net ionic: c. CH3CO2H and barium hydroxide Total: Net ionic: Reaction type: Reaction type: Reaction type:
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Photoelectric Effect and Light Light from a sodium vapor laser will not cause electrons to be ejected from a piece of calcium metal. The light from this laser has a frequency of 5.090 x 1014 Hz. a. The wavelength of the light is nm b. A photon of this light has energy J c. The work function of calcium is 2.24 eV. The longest wavelength of light that can cause photoelectric effect emission in calcium is nm
Spectroscopy Label EVERYTHING that can reasonably be labeled on the diagram below, including locations with letters: 12.
Simple Spectroscopy: Atomic Emission and Absorption Here is an energy level diagram for He+, a one electron species similar in all ways except nuclear charge to a hydrogen atom. From this set of 5 energy levels, only one transition will result in emission of light in the visible range, from about 400 nm to about 800 nm. Start by converting these wavelengths to photon energies.
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What transition is that? n=_____ to n=_____ What wavelength is that emission? = _____ nm It was (possibly) the absence of this wavelength, due to absorption, in the light from the sun that led to the discovery of helium. Cool.
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Polarity of Molecules and Bonds a. Circle the nonpolar molecule below:
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For the molecule circled above, draw a rotational isomer that is polar.
c. 15.
For the molecule with fluorine in it, circle the most polar bond(s) and draw an arrow to indicate the direction of their contribution to any molecular dipole moment the molecule might have.
Bonding in Big Molecules. Its the same as in small ones. The molecule below is aspirin (only one resonance structure shown):
How many sigma bonds, in total, are there in this molecule? How many pi bonds? _______ Identify the hybridization around the C and O atoms that have been numbered 1 - 4: C(1) _________ C(2) __________ C(3) ________ O(4) _________ Which carbon-carbon bond is stronger, a or b? ____ Which bond angle is larger, c or d? ____ Circle the most polar region(s) in the aspirin molecule. 16. Polarity Consider the species CSBr2, CSI2, COH2, and HBr. The first three all have essentially the same structure. Order them from lowest to highest polarity: < < <
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Phase Diagrams a. Label EVERYTHING, starting with the axes, that can reasonably be labeled on the phase diagram below. Assume that the pressure at the triple point is below 1 atm. 17. b. What evidence demonstrates that this cannot be the (simplified) phase diagram for water?
c.
Lay your pen(cil) across this graph f...