The Face-Centered Cubic (FCC) structure is popular because it packs atoms together very well. It has a packing factor of about 0.74, which means it uses space efficiently.

Here are some important points to know about FCC:

• Atomic Arrangement: In an FCC structure, atoms are placed at each corner of a cube and in the center of each of the cube's faces.

• Coordination Number: Each atom in the FCC connects with 12 other atoms. This helps make it more compact.

• Volume Calculation: We can find out how much space the atoms take up using this formula:

  $V_{\text{atoms}} = n \cdot \frac{4}{3} \pi r^3$

  Here, $n$ is 4, meaning there are 4 atoms in one FCC unit cell. The letter $r$ stands for the radius of an atom.

• Unit Cell Volume: The space inside the FCC unit cell can be calculated using:

  $V_{\text{cell}} = a^3$

  In this formula, $a$ is the length of one side of the cell and is equal to $2\sqrt{2}r$.

So, the great packing efficiency of the FCC structure comes from how the atoms are arranged and how they connect with each other.