Posted by **Z32** on Tuesday, September 15, 2009 at 1:16pm.

BCC crystal structure, atomic radius of .1363, and an atomic weight of 95.94g/mol. How would you compute the theoretical density?

- Science/math -
**DrBob222**, Tuesday, September 15, 2009 at 1:33pm
radius is 0.1363 WHAT? What unit?

- Science/math -
**DrBob222**, Tuesday, September 15, 2009 at 2:03pm
My best guess is that this is 136.3 pm which converts to 136.3 x 10^-9 m or 1.363 x 10^-8 cm.

Then d (the diagonal in the bcc) is

4r = 4 x 1.353 x 10^-8 = 4.452 x 10^-8 cm

and d^2 = 3a^2.

Solve for a and I get 3.148 x 10^-8 cm and volume is a^3 = ??

mass of unit cell is 2 atoms/unit cell x 95.94/6.022 x 10^23 = ??

Then density = mass/volume. I get about 10.2. Check my thinking. Check my arithmetic.

- Science/math -
**DrBob222**, Tuesday, September 15, 2009 at 3:13pm
You may want to note that I made a typo in converting pm to cm in the first step; however, the answer of 1.363 x 10^-8 cm is correct.

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