Misplaced Pages

Trigonal pyramidal molecular geometry

Article snapshot taken from Wikipedia with creative commons attribution-sharealike license. Give it a read and then ask your questions in the chat. We can research this topic together.
(Redirected from Trigonal pyramid) Molecular geometry with one atom at the apex and three atoms at the corners of a trigonal base
Trigonal pyramidal molecular geometry
ExamplesNH3
Point groupC3v
Coordination number3
Bond angle(s)90° to 109.5°
μ (Polarity)>0

In chemistry, a trigonal pyramid is a molecular geometry with one atom at the apex and three atoms at the corners of a trigonal base, resembling a tetrahedron (not to be confused with the tetrahedral geometry). When all three atoms at the corners are identical, the molecule belongs to point group C3v. Some molecules and ions with trigonal pyramidal geometry are the pnictogen hydrides (XH3), xenon trioxide (XeO3), the chlorate ion, ClO
3, and the sulfite ion, SO
3. In organic chemistry, molecules which have a trigonal pyramidal geometry are sometimes described as sp hybridized. The AXE method for VSEPR theory states that the classification is AX3E1.

Phosphine, an example of a molecule with a trigonal pyramidal geometry.

Trigonal pyramidal geometry in ammonia

The nitrogen in ammonia has 5 valence electrons and bonds with three hydrogen atoms to complete the octet. This would result in the geometry of a regular tetrahedron with each bond angle equal to arccos(−⁠1/3⁠) ≈ 109.5°. However, the three hydrogen atoms are repelled by the electron lone pair in a way that the geometry is distorted to a trigonal pyramid (regular 3-sided pyramid) with bond angles of 107°. In contrast, boron trifluoride is flat, adopting a trigonal planar geometry because the boron does not have a lone pair of electrons. In ammonia the trigonal pyramid undergoes rapid nitrogen inversion.

  • The electron pair arrangement of ammonia is tetrahedral: the two lone electrons are shown in yellow, the hydrogen atoms in white The electron pair arrangement of ammonia is tetrahedral: the two lone electrons are shown in yellow, the hydrogen atoms in white
  • The molecular geometry can be inferred from the electron pair arrangement, showing that ammonia has trigonal pyramidal geometry. The molecular geometry can be inferred from the electron pair arrangement, showing that ammonia has trigonal pyramidal geometry.

See also

References

  1. Cleeton, C. E.; Williams, N. H. (1934). "Electromagnetic Waves of 1.1 cm Wave-Length and the Absorption Spectrum of Ammonia". Phys. Rev. 45 (4): 234. Bibcode:1934PhRv...45..234C. doi:10.1103/PhysRev.45.234.

External links

Molecular geometry
Coordination number 2
Coordination number 3
Coordination number 4
Coordination number 5
Coordination number 6
Coordination number 7
Coordination number 8
Coordination number 9
Category: