SSI - symmetry

Question 1

symmetry operations definiton

Answer 1

actions that leave molecules looking the same after being done - these are how the symmetry of a molecule is assessed

Question 2

what are the 2 types of symmetry operations?

Answer 2

rotations and reflections

Question 3

rotation definition

Answer 3

rotating a molecule around a 1D axis of rotation

Question 4

reflection definition

Answer 4

reflecting a molecule through a 2D mirror plane

Question 5

symmetry element definition

Answer 5

the axis/plane in which the symmetry operation is performed

Question 6

practice: what symmetry elements do we expect from H2O?

Answer 6

H20 has 1 symmetrical rotation
- operation = C2 rotation
- element = C2 axis
and 2 symmetrical reflections
- operation = σv reflection
- element = σv mirror plane
and also E (mention for all molecules!!)

Question 7

what does σv represent?

Answer 7

σ is used for mirror plane reflections
v = vertical (includes principle axis C2)

Question 8

what does σh represent?

Answer 8

σ is used for mirror plane reflections
h = horizontal (perpendicular to principle axis C2)

Question 9

what does E mean?

Answer 9

identity operation E = doing nothing
all molecules have this!

Question 10

what does C2 mean?

Answer 10

C is used for rotations
2 is because 360/180 = 2, represents symmetry if molecule is rotated 180

Question 11

do all symmetry elements have to go through bonds?

Answer 11

no, but these are less obvious