quiz1fall2000 - 'I; *,fI!i"'\' 'if f'1, .J :)'~"...

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'I; *,fI!i""'\' 'if :)'~" 2.7 f'1, f""1t .J {"'c ~.~ ENGSC 3313, Fall 2000 Quiz 1 Name .nswer anv 4 questions only, 1 point each 1. An important radioactive isotope is strontium-90 because it is absorbed by bone (The Sr substitutes for Ca in C~(PO4)J. It has a half life of 30 years. What proportion would have decayed after 20 years? We have exponential decay e-tlA where A is a constant, Ao = initial amount (~) Substituting 0.5 = e-30/A and A = 43.5 years .~ Ao e-20/43.5 = Md Repeating Hence, proportion decayed is 1- 0.63 = ~ 2. Please write the expected ground state electron configurations for Cobalt (Co, element #27) and for Molybdenum (Mo, element #42) and answer the following questions. Would you expect Co and Mo to be in the same column of the periodic table? Why or Why not? Co: 182 282 2p6 382 3p6 482 3d7 QR Ca: [Ar] 482 3d7 Ma: 182 282 2p6 382 3p6 482 3dlo 4p6 582 4d4 QR Ma: [Kr] 5s2 4d4 Elements in the same column have electron configurations that end the same way. Since d' is not
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quiz1fall2000 - 'I; *,fI!i"'\' 'if f'1, .J :)'~"...

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