chemistry 12th class cbse notes

Parameters of Unit Cell

A unit cell is characterized by 6 parameters:

  • 3-edges a, b and c (refer the diagram given above). The edges may or may not be perpendicular to each other.
  • 3 angles α (between b and c), β(between a and c) and γ(between a and b).

Classification of unit cell:

Primitive Unit Cells:

When constituent particles are present only on the corner positions of a unit cell, it is called a primitive unit cell.

Centred Unit Cells:

When a unit cell contains one or more constituent particles present at positions other than corners in addition to those at corners, it is called a centred unit cell.

Centred unit cells are of three types:

Body-Centred Unit Cells:

Such a unit cell contains one constituent particle (atom, molecule or ion) at its body-centre besides the ones that are at its corners.

Face-Centred Unit Cells:

Such a unit cell contains one constituent particle present at the centre of each face, besides the ones that are at its corners.

End-Centred Unit Cells:

In such a unit cell, one constituent particle is present at the centre of any two opposite faces besides the ones present at its corners.

How useful was this post?

Click on a star to rate it!

Average rating 4.3 / 5. Vote count: 10

No votes so far! Be the first to rate this post.

As you found this post useful...

Follow us on social media!

We are sorry that this post was not useful for you!

Let us improve this post!

Tell us how we can improve this post? Please mention your Email so that we can contact you for better feedback.

Leave a Reply