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The seesaw geometry occurs when a molecule has a steric number of 5, with the central atom being bonded to 4 other atoms and 1 lone pair (AX 4 E 1 in AXE notation). An atom bonded to 5 other atoms (and no lone pairs) forms a trigonal bipyramid with two axial and three equatorial positions, but in the seesaw geometry one of the atoms is replaced ...
As described by the VSEPR model, the five valence electron pairs on the central atom form a trigonal bipyramid in which the three lone pairs occupy the less crowded equatorial positions and the two bonded atoms occupy the two axial positions at the opposite ends of an axis, forming a linear molecule.
For example, sulfur hexafluoride (SF 6) is an octahedral molecule. Trigonal pyramidal : A trigonal pyramidal molecule has a pyramid-like shape with a triangular base. Unlike the linear and trigonal planar shapes but similar to the tetrahedral orientation, pyramidal shapes require three dimensions in order to fully separate the electrons.
XeF 4, with square planar geometry, has 1 C 4 axis and 4 C 2 axes orthogonal to C 4. These five axes plus the mirror plane perpendicular to the C 4 axis define the D 4h symmetry group of the molecule. For linear molecules, either clockwise or counterclockwise rotation about the molecular axis by any angle Φ is a symmetry operation.
Some directions and planes are defined by symmetry of the crystal system. In monoclinic, trigonal, tetragonal, and hexagonal systems there is one unique axis (sometimes called the principal axis) which has higher rotational symmetry than the other two axes. The basal plane is the plane perpendicular to the principal axis in these crystal ...
Groups containing a polar axis are called polar. A polar crystal possesses a unique polar axis (more precisely, all polar axes are parallel). Some geometrical or physical property is different at the two ends of this axis: for example, there might develop a dielectric polarization as in pyroelectric crystals. A polar axis can occur only in non ...
In organic chemistry, molecules which have a trigonal pyramidal geometry are sometimes described as sp 3 hybridized. The AXE method for VSEPR theory states that the classification is AX 3 E 1. Phosphine, an example of a molecule with a trigonal pyramidal geometry.
C nv is C n with the addition of n mirror planes parallel to the axis of rotation. S 2n (for Spiegel, German for mirror) denotes a group with only a 2n-fold rotation-reflection axis. D n (for dihedral, or two-sided) indicates that the group has an n-fold rotation axis plus n twofold axes perpendicular to that axis.