Chem. Please help

Question

Explain why the coordination number for all the atoms in the bcc lattice is the same.

Answer 1

Let's start with the definition of coordination number ...

the number of atoms/ions immediately surrounding a central atom

simple cubic unit cell ... has atoms at each of 8 corners of the cube

body-centered cubic unit cell ... has atoms at each of 8 corners and one right at the center of the cube

face-centered cubic unit cell ... has atoms at each of 8 corners and atoms on each of 6 faces of the cube

Now, let's sit at one atom of each cell ... and determine how many are surrounding it

simple ... 6 ... left, right front, back, top bottom

body-centered ... 8 ... from the viewpoint of the one in the center, like sitting in the middle of a box

... so one atom at each of 8 corners surrounds it

face-centered ... 12 ... from the viewpoint of center of earth

... 4 in the northern hemisphere + 4 at the equator + 4 in the southern hemisphere

I think these pages have some nice images to help you visualize each.

https://msestudent.com/simple-cubic-unit-cell/

https://msestudent.com/body-centered-cubic-bcc-unit-cell/

https://msestudent.com/face-centered-cubic-fcc-unit-cell/