What Went Wrong with My Calculation for Iridium Atomic Radii?

[Taryn]

hey just wondering where I went wrong

Iridium Crystallizes in a face centred cubic unit call that has an edge length of 3.833A
The atom in the cantre of the face is in contact with the corner atoms

calculate the atomic radii of the irridium atom
I did this
using pythag, (3.833^2)+(3.833^2)=c^2
b^2= 29.384
b=5.42
Then I divided it by 2 as it was the radius and got 2.710
But I am assuming that this is wrong due to the qu asking for the atomic radii. So I divide it by 192.272 and I still get the wrong answer.
The answer is meant to be 1.355Angstrom

So if anyone could tell me where I went wrong I would be much appreciative
Thanks

 

[nazzard]

Hello Taryn,

try to revisualise one face. How many atom-radii will fit into the length of the face-diagonal? You are close to the correct answer.

Regards,

nazzard

 

[Taryn]

figured it out, u divide by 2 as the atomic radii is being asked for and there are two atoms. So simple!