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MSE 230 HW 1 Solutions Fall 2014

1. The main differences between the various forms of bonding are:

•  Ionic: there is an electrostatic attraction between oppositely charged ions. Non-

directional bonding.

• 

Covalent: there is electron sharing between two adjacent atoms such that each atomassumes a stable electron configuration. The bonds are directional.

•  Metallic: the positively charged ion cores are shielded from one another, and also

“glued” together by the sea of valence electrons. Non-directional bonding.

•  van der Waals: relatively weak secondary bonds, non-directional bonding.

2.

Both Young’s modulus and the coefficient of thermal expansion (CTE) depend on the strength of

bonding. Weakly bonded materials like polymers have small elastic moduli (low rigidity) and

large CTE’s while strongly bond ceramics have large elastic moduli and expand relatively little

upon heating.

0.0

100.0

200.0

300.0

400.0

500.0

0 20 40 60 80 100

   Y  o  u  n  g   '  s   M  o   d  u   l  u  s   (   G   P  a   )

CTE

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3. Callister Problem 2.23: Make a plot of bonding energy versus melting temperature for the

metals listed in Table 2.3. Using this plot, approximate the bonding energy for molybdenum,

which has a melting temperature of 2617°C.

Solution

Below is plotted the bonding energy versus melting temperature for these four metals.

From this plot, the bonding energy for molybdenum (melting temperature of 2617°C) should be

approximately 680 kJ/mol. The experimental value is 660 kJ/mol. Please note that you have to

assume that there is a linear relationship between melting temperature and bond energy