Symmetry in crystal structures-

In summary, the conversation is about understanding the different types of symmetry in crystal structures, including mirror planes, glide planes, screw axes, and centres of symmetry. The individual is seeking clarification on identifying these symmetries in a given diagram and understanding the concept of inversion. They are also asking for assistance in understanding crystals and their properties.
  • #1
Claire84
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Symmetry in crystal structures- please help!

Hi there, I was hoping someone here could help explain a few things about crystal symmetry to me cos it hs me so confused (we've been doing crystals for 2 weeks and things up til now have been ok, I'm just getting myself muddled as usual!). The attachment is of the diagram handed out with our assignment this week and for one of the questions we've to spot mirror planes, glies planes, screw axes and centres of symmetry.

All I've come up with so far has been 2 mirror planes marked in red, 2 screw diads marked in red splodges, 2 diagonal glide planes marked in blue (with translation in the plane of the paper), a centre of symmetry marked in purple and 3 glide planes marked in green (translation both perpenciular and parallel to the plane of the page). I'm really unsure about my glide planes though because can they just go straight through the atoms like that (I'm talking about the ones marked in blue).? The ones we've covered in lectures have always ran between 2 sets of atoms, not up the middle of some of them (like can you not have this because it'd be like cutting the atom in half and translating it?!). Also, have I got my centre of symmetry right? Could someone maybe give me a good description of what it actually is? We have a definition of it with inversion in it, but I don't really get inversion (yet another thing that would be great if someone could explain).

If anyone could give me a hand at all with this or let me know where I'm going wrong etc, I'd be really grateful. At the moment all I seem to be doing is reading about crystals and actually having someone to sort out a few of the bits and pieces I'm stuck on would be fantastic. Thanks.

Claire :eek:
 

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  • #2
Mirror Planes: A mirror plane is a plane of symmetry in a crystal structure that reflects the atoms in the structure when viewed from one side, as if looking in a mirror. Glide Planes: A glide plane is a plane of symmetry in a crystal structure that reflects the atoms in the structure when viewed from one side, and then translates them a certain distance along the plane. Screw Axes: A screw axis is an axis of symmetry in a crystal structure that rotates the atoms in the structure around the axis by a certain amount. Centres of Symmetry: A centre of symmetry is a point in a crystal structure where all the atoms in the structure are inverted in position after a certain rotation has been applied. Inversion is a transformation where the orientation of each atom is reversed.
 

1. What is symmetry in crystal structures?

Symmetry in crystal structures refers to the repeating arrangement of atoms or molecules in a crystal lattice. This symmetry is described by a set of mathematical operations, such as rotations, reflections, and translations, that when applied to the crystal, results in the same pattern.

2. Why is symmetry important in crystal structures?

Symmetry is important in crystal structures because it helps to determine the physical and chemical properties of a crystal. It also allows for the prediction of crystal behavior and the understanding of crystal formation and growth.

3. How is symmetry in crystal structures determined?

Symmetry in crystal structures is determined by using techniques such as X-ray crystallography, neutron diffraction, or electron microscopy. These methods allow scientists to study the arrangement of atoms in a crystal and determine the type and degree of symmetry present.

4. What are the different types of symmetry in crystal structures?

There are several types of symmetry in crystal structures, including translational symmetry, rotational symmetry, mirror symmetry, and inversion symmetry. These different types of symmetry are classified and described by the crystallographic point groups and space groups.

5. How does symmetry affect the physical properties of crystals?

The symmetry of a crystal has a direct impact on its physical properties, such as melting point, hardness, and optical properties. This is because the arrangement of atoms in a crystal lattice determines how the crystal will interact with external forces, such as heat, pressure, or light.

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