Question

In: Chemistry

If an object is at point x,y,z (Cartesian coordinates) and its symmetry mate is related by...

If an object is at point x,y,z (Cartesian coordinates) and its symmetry mate is related by a 21 screw axis, what is the location in Cartesian coordinates for the symmetry mate?

Solutions

Expert Solution

Hello!!

A screw axis is a symmetry operation in which rotation is followed by translation i.e. you first rotate the object by an angle and then translate it in a perpendicular direction by a distance 1/a. Assume the screw axis to be na axis, then here, = 360/n and the translation is to be made in the perpendicular direction by 1/a. You can consider it to be absolutely similar to a screw (hence getting its name).

Here, for 21 screw axis, the object has to be rotated by an angle of 360/2= 180o followed by a translation of 1/2.

Thus, in your case, for a 21 screw axis, if we consider c-axis as our axis of rotation, the object will change its coordinates from (x,y,z) to (-x,-y,z) upon a 180o rotation because for 180o rotation, the cartesian coordinates remains the same for the direction of the axis and they are inverted for the other 2-axis. This will further be followed by a translation of 1/2 along c-axis.

Finally,

Feel free to ask any of your queries in the comments.


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