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 /4 Question /8 Question 3 /1 Question 4 /1 Question 5 /1 Question 6 /1 Question 7 /8 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, drw one vlid Lewis structure, which need not be the best structure. Next, indicte the three-dimensionl geometry by both drwing its VSEPR structure nd by providing the nme for the geometry round the underlined centrl tom. Then, predict whether the molecule or ion is polr or is non-polr. Finlly, give the idelized bond ngles for the stted bonds bsed on your VSEPR structure; 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 Drw the Lewis Structure Drw nd Nme Bonding Geometry Is it Polr or Non-Polr? Idel Bond Angle(s) for O S O is (re) SO O S O (is) re SO3 F S F is (re) SF5 + Problem. The triiodide nion, I3, is liner. The corresponding nion of fluorine, F3, however, does not exist. In 1 3 sentences, explin why it is impossible for n nion of F3 to form.

3 Problem 3. The element Z, which is n element in the first three rows of the periodic tble, forms the molecule ZFO with trigonl pyrmidl bonding geometry round Z. In ddition, the length of the Z O bond suggests it hs bond order greter thn 1 but less thn. Identify Z nd, in 3 sentences, explin how you rrived t your identifiction. Problem 4. Consider the ion NF +, which hs skeletl structure of N N F. Drw ll possible resonnce structures for this ion nd nnotte ech of your structures with the forml chrge for ech tom. Circle the resonnce structure bove tht provides the best overll picture of the bonding for NF + nd in no more thn two sentences, explin your reson for selecting this resonnce structure.

4 Problem 5. The underlined centrl tom for two of the nions below use identicl hybrid orbitls to form bonds with the nion s other toms; the remining nion uses different set of hybrid orbitls. Circle the nion tht is different nd, in 3 sentences explin the reson for your choice. As prt of your nswer, identify the specific hybrid orbitls used by ech nion s centrl tom. NO CO3 BF4 Problem 6. Moleculr orbitls form when tomic orbitls interct with ech other. Consider the three p-orbitls on nitrogen. When these orbitls interct with the three p-orbitls on nother tom of nitrogen to form N, the resulting moleculr orbitls re of four types: sigm bonding, sigm ntibonding, pi bonding, nd pi ntibonding. For ech of these four types of moleculr orbitls, drw picture in the tble below tht shows how the electrons re distributed in spce reltive to the two nitrogen toms. sigm bonding sigm ntibonding pi bonding pi ntibonding

5 Problem 7. Consider the led hlides PbF, PbCl, nd PbBr. Which of these compounds likely hs the highest melting point? Explin your resoning in 1 sentences. Problem 8. The figure below shows three cross-sections through the lttice structure for solidstte compound tht consists of rhenium ions nd oxide ions. From left-to-right, these cross-sections re t z = 0, 0.5, nd 1. Wht is the empiricl formul for rhenium oxide. Be sure tht how you rrived t your formul is cler by nnotting the figure bove to show the contribution of ech ion. The chemicl symbol for rhenium is Re. Bsed on your empiricl formul, wht is the chrge on the rhenium ion? In one sentence, explin how you rrived t your nswer. Wht kind of lttice structure do the rhenium ions exhibit? In one sentence, explin how you rrived t your nswer. In wht kind of holes within the oxide lttice re rhenium ions found? In one sentence, explin how you rrived t your nswer. Wht is coordintion number for the oxide ions reltive to the rhenium ions? In one sentence, explin how you rrived t your nswer.