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1 Nme Chem 130 Second Exm On the following pges re eight questions tht consider 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 /1 Question 6 /1 Question 7 /1 Question 8 /10 Totl /100 Some potentilly useful equtions nd constnts re provided here. A periodic tble nd other potentilly useful dt re provided on seprte hndout. Potentilly Useful Equtions 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 - Potentilly Useful Constnts c = m/s h = Js N A = mol 1 Plese write netly!

2 Problem 1. For ech of the following molecules or ions, drw ny one vlid Lewis structure of your choosing (it need not be the best structure). Provide the nme for the bonding geometry round the underlined centrl tom, predict whether the molecule or ion is polr (P) or non-polr (NP), nd provide the idelized bond ngle for the stted bond. Use the spce t the bottom of the pge to work out your structures nd then plce the result in the tble. Molecule or Ion Lewis Structure Bonding Geometry Polr or Non-Polr? Idel Bond Angle for n O S O SO 3 IO F n O I O SbO 4 3 n O Sb O Spce for work (will exmine if included, but not evluted for credit).

3 Problem. The compound ZFO, in which Z is the centrl tom, is known to hve trigonl pyrmidl geometry. In ddition, the length of the ZO bond suggests its bond order is greter thn one but less thn two. Identify n element tht might serve s Z nd in no more thn -3 sentences, explin how you rrived t your choice of element. Problem 3. Consider the ion N I +, which hs skeletl structure of N N I. Drw ll possible resonnce structures for this ion nd nnotte your structures with the forml chrges for ech tom. Circle the resonnce structure tht provides the best overll picture of the ion s bonding nd, in no more thn -3 sentences, explin your reson for picking this structure. Problem 4. A bond s dissocition energy is the energy needed to brek the bond, with stronger bonds hving more positive bond dissocition energy. Consider the following three ions, ech of which consists of just bonds between nitrogen nd oxygen. Drw Lewis structures below ech ion nd then rnk the ions from the wekest NO bond to the strongest NO bond. In no more thn -3 sentences, explin the reson for your rnking. NO + NO NO 3 the wekest NO bond is in: the strongest NO bond is in:

4 Problem 5. Shown to the right is moleculr orbitl digrm for the ion OCl +. Complete the digrm by () identifying which element is on ech side of the digrm, writing your nswers in the vilble boxes; (b) plcing the vlence electrons for ech tom in the pproprite tomic orbitls, giving thought to which element crries the positive chrge; nd (c) filling in the electrons for the ion s moleculr orbitls. Bsed on your moleculr orbitl digrm, wht is the bond order for OCl +? Is OCl + prmgnetic or dimgnetic ion (circle your nswer below)? In no more thn 4-5 sentences, clerly explin the resons for your nswers, including how you identified the correct loction for ech element nd the element to which you ssigned positive chrge. 3p the element on this side is 3s σ p π * p π p σ p σ s the element on this side is s p The bond order for OCl + is. σ s OCl + is: prmgnetic dimgnetic Problem 6. The three compounds listed below generlly re considered covlent; ech, however, hs some ionic chrcter. Rnk the compounds from the one with the lest ionic chrcter to the one with the most ionic chrcter nd, in -3 sentences, explin how you rrived t your rnking. HCl ICl SCl the compound with the lest ionic chrcter is: the compound with the most most ionic chrcter is:

5 oxygen Problem 7. Consider the series of led hlides given below. Rnk them from lowest melting point to highest melting point nd in -3 sentences explin the reson for your rnking. PbF PbCl PbBr the compound with the lowest melting point is: the compound with highest melting point is: Problem 8. Shown below re three cross-sections through the minerl potssium niobte, whose opticl properties mke it useful in the production of lsers. z = 0 z = 0.5 z = 1 oxygen potssium niobium Accounting only for ech tom s contribution to the unit cell shown bove, how mny complete oxygen (O), potssium (K), nd niobium (Nb) toms mke up unit cell? Plce your nswers in the spces below nd explin in -4 sentences how you rrived t your formul; you my find it helpful to nnotte the figure bove to identify toms by their possible loctions in the unit cell: corner, edge, fce, nd interior. the unit cell hs toms of oxygen the unit cell hs toms of potssium the unit cell hs toms of niobium