Unformatted text preview: l. Cobalt has a cubic closest packed structure. The cobalt atomic radius
is 125 pm. What is the density. A cubic closest packed stiucture is face—centered cubic. So .12 + l2 = (402
And 13 is the volume of 4 atoms (4 atoms since it is facecentered cubic)
Density his mass over volume. So l=r\/8 : 125 x [8 : 353.55 pm 13 a 4.4194 x 107pm3 convert this to cm3 12 4.4194X107pm3x(10 m)3x( C31 )3
pm 10 “m
1 4.4194x107 xl 0—36 x em3 = 4.4194X10"2?cm3 10"6
Now we need the mass of four atoms. 4 atoms Co x l mole/6.022 X 1023 atoms X 58.9332 g/mole =
3.9145 x 10’22 grams Density is g/cm3 so = 3.9145 x lO'ZZg/4.4194 x 10'23 cm3 = 8.86 g/cm3 2. Nickel has a facecentered cubic unit cell. The density of nickel is
6.84 g/mL. Calculate the value for the atomic radius of nickel. We are given density, we can ﬁnd the molar mass and ﬁnd the mass of four atoms. From the mass of four atoms, we can ﬁnd the volume of
four atoms and then we have the length of the cube since we take the cube root of the volume. Once we have the length, r is the length
divided by root 8. Ni 58.6934 g/mole 4 atoms x lmole/6.022 x 1023 atoms x 58.6934g/mole = 3.8986 x 10.22 g
3.8986 x 10'23g/6s4g/mL = 5.70 x 10'23 mL Taking the cube root 113848 X 10'8 cm Dividing by the root of s to give 1’ = 1.36 x 10'8 cm Converting cm to pm x 10‘2 divided 10”12 t 136 pm ...
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 Fall '08
 dockery
 Chemistry

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