How many atoms are in the unit cell of graphite?

In summary, the unit cell of graphite has a hexagonal crystal structure with a basis of 2 atoms. However, due to the structure's oppositely sloped ends and lack of atoms in the center, there are only 4 atoms in the unit cell. This is different from the hexagonal close packed structure, which has 6 atoms in the unit cell.
  • #1
stunner5000pt
1,461
2

Homework Statement


How many atoms are there in the unit cell of graphite?


2. The attempt at a solution
I know graphite is hexagonal crystal structure. hcp

also know that hcp has basis of hexagonal lattice which as 2 basis atoms.

is there some other info i need because the answer is supposed to be 4...

Thanks for your help
 
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  • #2
I'm not an expert so don't blindly trust my answer, but I believe that the unit cell for graphite may be twice as high, due to oppositely sloped ends of the structure. There are also no atoms in the center of the lattice (as in, the lattice would be a "hollow hexagonal pipe" of atoms). Therefore, you have (1/6)12 on the top and bottom, + (1/3)6 at the middle. This adds up to four.
http://www.chem.ox.ac.uk/icl/heyes/structure_of_solids/Lecture1/Lec1.html (the picture of the 3D graphite structure is almost halfway down the page).

I don't think your graphite structure is HCP. HCP (Hexagonal close packed) actually adds up to 6, since it has 3 atoms fully contained, then 12(1/6) + 2(1/2). Of course, there are other variants of hexagonal which have less. For instance, I think there was one called Simple Hexagonal somewhere here: http://www.chem.lsu.edu/htdocs/people/sfwatkins/ch4570/lattices/lattice.html

(SH should be 3 atoms...and that is also not the same as the graphite lattice ether because it has the half atoms at the end center in addition to not having the sloped top and bottom)
 
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Related to How many atoms are in the unit cell of graphite?

1. What is a hexagonal crystal structure?

A hexagonal crystal structure is a type of atomic arrangement in solid materials that is characterized by sixfold symmetry around a central axis. It is one of the seven main crystal systems and is commonly found in minerals, metals, and other materials.

2. How is a hexagonal crystal structure formed?

A hexagonal crystal structure is formed when atoms or molecules arrange themselves in a repeating pattern with six sides and six angles, forming a hexagonal prism. This arrangement is favored due to the efficient packing of atoms and the strong bonds between them.

3. What are the properties of a hexagonal crystal structure?

Some common properties of materials with a hexagonal crystal structure include high strength, anisotropic behavior (different properties in different directions), and resistance to shear stress. These materials also tend to have high melting points and good electrical conductivity.

4. What are some examples of materials with a hexagonal crystal structure?

Some examples of materials with a hexagonal crystal structure include graphite, quartz, beryl, and ice. Many metals, such as titanium and zinc, also have a hexagonal crystal structure in their pure form.

5. How is a hexagonal crystal structure different from other crystal structures?

The main difference between a hexagonal crystal structure and other crystal structures, such as cubic or tetragonal, is the arrangement of the atoms or molecules. In a hexagonal crystal structure, the atoms are arranged in a hexagonal prism, while in other structures, they may be arranged in a cube or a parallelepiped. This results in different physical and chemical properties for each type of crystal structure.

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