 Okay, so let's try this one. It says, silver crystallizes with a face-centered cubic unit cell 0.407 nanometers on an edge. Calculate the atomic radius of silver. So, remember, face-centered cubic atoms on each one of the corners, but also atoms on each one of the faces. Okay, so when we do this one, you've got to remember the formula. So it's 4S or R. So it gives us, in this case, S, right? Because it says that the unit cell has 0.407 nanometers on an edge. So that edge is going to be S, 0.407 nanometers. Okay, and we can actually just do this in nanometers because it doesn't give us any instructions as to what unit it wants its radius in. So the radius of silver is going to be S square root of 2 divided by 4. Let's put it in picometers just for fun. But since we said picometers, let's convert it into picometers. So a good conversion to remember is one nanometer is 100 picometers. Any questions on that one? In your unit, you might see these in its angstroms, and that's 1 times 10 to the negative 10. So it's another length.