Chem 130 Second Exam

Transcription

1 Nme Chem 130 Second Exm On the following pges you will find questions tht cover the structure of molecules, ions, nd solids, nd the different models we use to explin the nture of chemicl bonding. Red ech question crefully nd consider how you will pproch it before you put pen or pencil to pper. If you re unsure how to nswer one question, then move on to nother question; working on new question my suggest n pproch to the one tht is more troublesome. If question requires written response, be sure tht you nswer in complete sentences nd tht you directly nd clerly ddress the question. Question 1 /18 Question /1 Question 3 /1 Question 4 /1 Question 5 /14 Question 6 /10 Question 7 /10 Question 8 /1 Totl /100 Some potentilly useful equtions nd constnts re provided here. A periodic tble nd other potentilly useful dt re provided on seprte hndout. c = ln E = hn KE = hn W 1 = l æ 1 nm ç - è n1 n - 1 ö ø V Q $Q d AVEE = xie. + yie 1 + zie 3 x + y + z (vlence shell electrons only) FC = B æ EN V - N ö δ = - - ç V N B è EN + EN b ø - c = m/s h = Js N A = mol 1

2 Problem 1. For ech of the following molecules or ions, drw one vlid Lewis structure, which need not be the best structure. Give the nme for the bonding geometry round the underlined centrl tom, predict whether the molecule or ion is polr or is non-polr, nd give the idelized bond ngles for the stted bonds; if there is more thn one possible bond ngle, then list ech unique bond ngle nd nnotte your Lewis structure to indicte which is which. Your nswers for these lst two items must be consistent with the bonding geometry you identify. Molecule or Ion Lewis Structure Bonding Geometry Polr or Non-Polr? Idel Bond Angles for F S F re. SF4 Cl O Cl re. OCl F Xe F re. XeF5 + Problem. The ction [HCNXeF] + is interesting both becuse it is n exmple of species tht includes n element, Xe, normlly thought of s inert, nd becuse it is perfectly liner; tht is, the HCN, CNXe, nd NXeF bonds ll hve bond ngles of 180. Drw Lewis structure for this ction tht explins this liner structure nd identify the element tht crries the positive chrge.

3 Problem 3. The bicrbonte ion is HCO3, where ech oxygen is ttched to the crbon. As written, the formul lso seems to suggest tht the hydrogen is ttched to the crbon when ctully it is ttched to one of the three oxygens. Using one or more of the bonding models developed in this unit, present convincing rgument tht the hydrogen is ttched to the oxygen nd not to the crbon. Your written response should require no more thn single prgrph of 3 5 sentences, ccompnied with suitble sketches. Problem 4. Fulminte, CNO, is prticulrly unstble nion whose mercury slt is used s the explosive compound in blsting cps. Drw ll possible resonnce structures for the fulminte nion nd report the forml chrge on ech tom in ech structure. The bonding frmework for fulminte is C N O. Which of your resonnce structures provides the best picture of the bonding in fulminte? Circle your choice bove nd then explin your resoning below in 1 sentences. The most importnt resonnce structure for cynte, OCN, hs single bond between the oxygen nd the crbon, nd triple bond between the crbon nd the nitrogen. Using your resonnce structures for fulminte nd the informtion here bout cynte, provide 1 sentence explntion for why fulminte is so explosive while cynte is very stble.

4 Problem 5. Sulfur monoxide, SO, is simple inorgnic molecule tht is stble t very smll concentrtions only. It is rrely found on erth, but is found in vriety of interstellr environments, including the tmospheres of Io, one of Jupiter s moons, Venus, nd the Hle-Bopp comet. The vlence-shell moleculr orbitl digrm for SO is shown on the right. Complete the moleculr orbitl digrm by () identifying which tom is on the left side nd which is on the right side, (b) lbeling the vlence-shell tomic orbitls with their pproprite ns nd np designtions, (c) dding the pproprite number of electrons to the tomic orbitls, nd (d) dding the pproprite number of electrons to the moleculr orbitls. σ π π σ π π σ σ With respect to (), in 1 sentences, explin how you determined which set of tomic orbitls belongs to sulfur. With respect to (d), bsed on your moleculr orbitl digrm, wht is the bond order between sulfur nd oxygen? Does this gree with the bond order predicted by Lewis structure? Be sure to support your nswers with suitble structures, clcultions, nd/or 1 3 sentence explntion. With respect to (d), wht, if nything, cn you conclude bout the bility of SO to interct with n pplied mgnetic field. Explin your resoning in 1 sentences. Problem 6. Consider the following three ionic compounds: MgF, SrF, nd BeF. Which of these compounds hs the lrgest melting point? Briefly justify your choice in 4 sentences.

5 Problem 7. The figure below shows nine cross-sections through the unit cell of compound tht consists of cerium (Ce: solid blck spheres), gold (Au: speckled spheres), nd silicon (Si: solid white spheres), where the left side is the bottom of the unit cell nd the right side is the top of the unit cell (the vlues for z re, left-to-right, 0, 0.15, 0.50, 0.375, 0.500, 0.65, 0.750, 0.875, nd 1.00). The compound is of interest becuse of its mgnetic nd superconducting properties. Using this unit cell, wht is the simplest formul for this compound. Be sure tht it is cler how you rrived t your formul. Problem 8. Shown below is list of hypotheticl elements long with their electronegtivities nd possible chrges (note tht ech element lso hs possible chrge of zero). element Ax Ay Cy Cg Ny Kt Wt Lt Bt Z Tx electronegtivity chrges (0, ) , , Using the informtion in this tble, give the formul of () the most ionic-like compound, (b) the most metllic-like compound, nd (c) the most covlent-like compound. Ech of your three compounds must contin two different elements. In no more thn three sentences, explin the resoning behind your choices.