Are the properties of a crystal and its unit cell same?

In summary, the teacher's statement about analyzing the properties of a crystalline solid by looking at the properties of a unit cell does not contradict the fact that crystalline solids can have different properties in different directions, as the unit cell itself can exhibit anisotropic behavior. Additionally, while undergraduate courses often focus on cubic lattices, there are many other crystal structures with different symmetries, such as tetragonal and orthorhombic structures.
  • #1
Elena14
52
1
1) My teacher said that to analyze the properties of entire crystalline solid, we just need to analyze the properties of a unit cell, which is the smallest repeating unit of a crystalline solid.

2) But crystalline solids are known to be anisotropic, i.e. they have different properties in different directions.

Are not these two statements contradicting?
 
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  • #2
Elena14 said:
1) My teacher said that to analyze the properties of entire crystalline solid, we just need to analyze the properties of a unit cell, which is the smallest repeating unit of a crystalline solid.

2) But crystalline solids are known to be anisotropic, i.e. they have different properties in different directions.

Are not these two statements contradicting?
The unit cell can be anisotropic, look at the tetragonal crystal structure for instance, the c axis is stretched relative to the a and b axes. Typically undergraduate courses only ever deal with cubic lattices, as they are easier to solve, but there are many other structures, with different symmetries.
Equally you can have an orthorombic crystal, where one of the angles is not 90 degrees.
 
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Related to Are the properties of a crystal and its unit cell same?

1. What is a crystal?

A crystal is a solid material with a regular, repeating arrangement of atoms or molecules. This regular arrangement gives crystals their characteristic shape and properties.

2. What is a unit cell?

A unit cell is the smallest repeating unit of a crystal's lattice structure. It is a simple geometric shape that, when repeated in three dimensions, makes up the entire crystal.

3. Are the properties of a crystal and its unit cell the same?

No, the properties of a crystal and its unit cell are not necessarily the same. While the unit cell determines the overall structure of the crystal, the properties of a crystal are influenced by other factors such as impurities, defects, and external conditions.

4. How are the properties of a crystal and its unit cell related?

The properties of a crystal are determined by its unit cell, as the arrangement of atoms in the unit cell dictates the overall structure of the crystal. However, as mentioned before, other factors can also affect the properties of a crystal.

5. Can two different crystals have the same unit cell?

Yes, it is possible for two different crystals to have the same unit cell. This is known as isomorphism, where different chemical compounds can have the same crystal structure but different chemical compositions.

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