3 Content Board exercise: How to draw 3D models (molecules / crystals) Group work: each group gets a molecules name -> draw the structure, build a model, find symmetry elementsPoint Groups for molecules and crystalsFlow Chart to find a Point Group Practise with the molecules beforemyphayao.com: online quiz and tutorials
4 Symmetry Elements E - the identity operation Cn - rotation by 2π/n angle *Sn - improper rotation (rotation by 2π/n angle and reflection in the plane perpendicular to the axis)σh - horizontal reflection plane (perpendicular to the principal axis) **σv - vertical reflection plane (contains the principal axis)σd - diagonal reflection plane (contains the principal axis and bisect the angle between two C2 axes perpendicular to the principal axis)* - n is an integer ** - principal axis is a Cn axis with the biggest n. Molecule belongs to a symmetry point group if it is unchanged under all the symmetry operations of this group.
7 Group work:Draw and build these molecules Find symmetry elements and point groupsAcetoneChloromethaneSulfur chloro pentaflourideEtheneCyclopropanePlatinum tetrachlorideEthanediolPropadieneHydrogenperoxideMethanol
22 Order of Symmetry= the number h of symmetry elements for one point group !For example:Ammonia = C3v has order 6 (E + 2 C3 + 3 sv)The higher the order, the higher the symmetry !Which one has higher symmetry:C4v or D2h ?
23 End of Part 1 about Symmetry Point Groups For a molecule (or any structure) we can find symmetry operations which leave the molecule unchanged.These operations are:Identity E (for each molecule)Rotations CnMirrors σInversion i... And the combination Sn (combine Cn + σ )The sum of all possible operations for a molecule define its point group.The name of the point group indicates the main symmetry elements: for example: D4h indicates a C4 axis and σh)Try the program at “3DSymm” to see the symmetry operation in 3D