[lavender]

hi every body.
l am preparing for chemical test but i faced lots of problem? could u help me
. how do we know which of the compound is  threefold symmetry axis?

is there any chat in chemicsl subject?

[gentoo]

If you can rotate it 180 degrees around all three axes (x,y,z) and it is exactly the same, it has threefold symmetry.

[lavender]

Thanx for the answer>
   the question is:
 
which of the following does not have a threefold rotational symmetry axis?
BCL3
CH4
NH3
CCLF3
CLF3
 with drawing to explain*-*

[sjb]

If you can rotate it 180 degrees around all three axes (x,y,z) and it is exactly the same, it has threefold symmetry.

No, this means it has 3 two-fold axes.

[sjb]

Thanx for the answer>
   the question is:
 
which of the following does not have a threefold rotational symmetry axis?
BCL3
CH4
NH3
CCLF3
CLF3
 with drawing to explain*-*

Can you draw the structures of all of these, or perhaps describe how you would determine shape?

[gentoo]

Ah, I misunderstood the question.  Threefold symmetry is when the structure is the exact same each time you rotate it 120 degrees.

[lavender]

i think we ve first to draw VSEPR for the compounds
but i dont know how do we know the angles of threefold