Symmetry Elements of XeF4: Meaning of 2C2 & σh

In summary, XeF4 has D4h symmetry, which is pretty high, so there are a lot of elements. The 2C2 notation means that there are 2 C2 axes perpendicular to the principal axis .. there are actually two sets of these, which is why there is a primed and double-primed notation as well. The σh notation just means that there is a plane of symmetry perpendicular to the principal axis. Ah right, thanks a lot. Is there a sure shot way to know which is the principle rotation axis? For example in XeF4 why is the C4 the principle rotation axis? Why not the C2 axis perpendicular to it or why not the C2 rotation axis that goes from
  • #1
ampakine
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In my lecture notes the symmetry elements for XeF4 are listed as:
[PLAIN]http://img690.imageshack.us/img690/7216/syms.png [Broken]
but nowhere does it explain what 2C2 or σh means. What are these symmetry operations?
 
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  • #2
ampakine said:
In my lecture notes the symmetry elements for XeF4 are listed as:
[PLAIN]http://img690.imageshack.us/img690/7216/syms.png [Broken]
but nowhere does it explain what 2C2 or σh means. What are these symmetry operations?

Well, XeF4 has D4h symmetry, which is pretty high, so there are a lot of elements. The 2C2 notation means that there are 2 C2 axes perpendicular to the principal axis .. there are actually two sets of these, which is why there is a primed and double-primed notation as well. The σh notation just means that there is a plane of symmetry perpendicular to the principal axis.
 
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  • #3
Ah right, thanks a lot. Is there a sure shot way to know which is the principle rotation axis? For example in XeF4 why is the C4 the principle rotation axis? Why not the C2 axis perpendicular to it or why not the C2 rotation axis that goes from one F to the other F diagonally opposite it?

Also I didn't want to start a new thread for this so I'll ask it here. In MO theory for octahedral coordination complexes there are 6 ligand atomic orbitals which split into 3 sets of degenerate orbitals: a1g, t1u and eg. I keep seeing them referred to as symmetries. Does this mean the orbitals in these sets have a distinct shape or something? Are these point groups? I found this diagram:
[PLAIN]http://img852.imageshack.us/img852/6572/symm.png [Broken]
but I'm not too sure what to make of it. I can see how each of the ligand orbitals corresponds to a 4s, 4p or an eg d orbital and I'm guessing these are the orbitals that they merge with to form MOs but I'm pretty confused about the shapes of these ligand orbitals. Does the t1u orbital have 6 lobes or something?
 
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1. What are the symmetry elements of XeF4?

The symmetry elements of XeF4 are the identity element (E), two-fold rotation axis (2C2), and horizontal mirror plane (σh).

2. What does 2C2 mean in the context of XeF4?

2C2 refers to a two-fold rotation axis, which is a symmetry element that indicates the molecule can be rotated 180 degrees around an axis without changing its appearance.

3. What is the significance of σh in the symmetry elements of XeF4?

σh represents a horizontal mirror plane, which is a symmetry element that divides the molecule into two equal halves that are mirror images of each other.

4. How do these symmetry elements affect the properties of XeF4?

The symmetry elements of XeF4 dictate its overall shape and orientation in space, which can affect its physical and chemical properties.

5. Why is it important to understand the symmetry elements of XeF4?

Understanding the symmetry elements of XeF4 allows scientists to predict its behavior and interactions with other molecules, which is crucial for studying its properties and potential applications.

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