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April 16, 2014

April 16, 2014

Posted by **Angie** on Saturday, November 14, 2009 at 11:50am.

- AP Chemistry -
**DrBob222**, Saturday, November 14, 2009 at 2:30pmbcc means 2 atoms per unit cell.

mass of unit cell is

2*55.847/6.022 x 10^23 = ?? g/unit cell.

mass = volume x density or

volume = mass/density = ??g/7.86 g/cc = xx cc

a (the edge length) = volume^{1/3}

for a bcc crystal, radius = (a/4)*3^{1/2}. Check my thinking. I obtained 2.87 x 10^-8 cm for the radius. Check my arithmetic and algebra.

- AP Chemistry -
**DrBob222**, Saturday, November 14, 2009 at 2:42pmFor the volume occupied, find the volume of the atoms (4/3)*pi*r^3 (you know r from the first calculation to be 1.24 x 10^-8 cm). Multiply that volume by 2 (because there are 2 atoms/unit cell), then divide by the volume of the unit cell (which I found to be 2.36 x 10^-23 cc) which gives 67.7% which rounds to 68% of the space actually occupied by the atoms. The other 32% is space.

- AP Chemistry--correction -
**DrBob222**, Saturday, November 14, 2009 at 2:52pmI quoted radius above that obtained 2.86 x 10^-8 but that isn't what I found. I found radius of the iron atom to be 1.24 x 10^-8 cm.

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