g-chem question

[howui3]

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How many atoms are there, respectively, in the bodycentered
cubic, face-centered cubic, and simple cubic
unit cells?
A. 1; 2; 3
B. 1; 2; 4
C. 2; 3; 1
D. 1; 4; 2
E. 2; 4; 1


never seen anything like this.....should i even bother understanding this?

thanks

 

[lisat]

How many atoms are there, respectively, in the bodycentered
cubic, face-centered cubic, and simple cubic
unit cells?
A. 1; 2; 3
B. 1; 2; 4
C. 2; 3; 1
D. 1; 4; 2
E. 2; 4; 1


never seen anything like this.....should i even bother understanding this?

thanks

Yeah, it's pretty simple, so it can't hurt right? Unit cells are mentioned in the Kaplan book, so they must be pretty basic. The three different unit cells are just different forms that solid atoms can take.

Each form represents a cube and where atoms are. The easiest one is the simple unit cell. In that one, there are spheres (which represent atoms at each corner of the cube), but since a unit cell is only the cube and not beyond the cube, you only count 1/8th of each atom. 8 corners * 1/8 atom at each corner = 1 atom.

Now the other two unit cells are more complex versions of the simple one. The body centered unit cell still has the atoms at the corners but as the name implies, there's also one directly at the center. That's 1 atom from the corners + 1 in the center = 2 atoms.

The last is the face centered unit cell. Again it has the atoms at the corners but this one, again as the name implies has atoms on each face. Now only half of the atom is actually included in the cell (the other half sticks out). That's 1 from the corners + 1/2 atom at each face * 6 faces = 4 atoms!

And that's it. It's pretty easy to remember which unit cell's which. I hope I wasn't too confusing. Good luck! 😳

 

[howui3]

thanks for the help..... not as bad as i thought

 

[dexadental]

Couldn't have explained it much better...