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mid+term+1+first+draft(2) - tDEC-211 MidTerm#1 Name Section...

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tDEC-211: MidTerm #1 Name:_________________________ Section_______ Spring 2007 M. W. Barsoum (Print) 60 mins. Closed-book, closed-notes exam. Formulae given on attached sheet (see last page). You may also use a calculator, periodic table and ruler. Please show all working for full credit. 1 . For the following questions choose the correct answer and fill in the blanks, as needed. i) For any bond to form, you need long/short (choose one) range attractions and/or (choose one) long/ short (choose one) range repulsions. If it were the other way round then no bond would form . 4 pts ii) The main reason water has a lower/higher (choose one) melting point than Al is because the strength of the hydrogen bonds holding the ice together are much weaker than the metallic bonds holding the Al atoms together in Al. 4 pts iii) In the zinc blende unit cell there are 4 cations and 4 anions because (show calculations, etc.). 1/8*8 + 6*1/2 = 4 (for anions) and 4*1 = 4 (for cations) . 4 pts. iv) Metallic bonds usually occur between atoms that are weakly/ strongly (choose one) electropositive. Metallic bonds are characterized as having localized/ delocalized (choose one) electrons. The best evidence for this conclusion is seen in (pick a property) _ high_conductivity or low resistivity_______________________ 3 pts v) The bonding in MgO and NaCl is mainly ionic. The melting point of MgO is higher/lower (choose one) than that of NaCl because (explain with equation) bond energy z 1 z 2 is
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