Trigonal Pyramidal

Definition

Trigonal pyramidal is a molecular geometry in which a central atom is bonded to three atoms and one lone pair of electrons, resulting in a pyramid-like shape. This geometry is commonly observed in molecules and is an important concept in the understanding of Lewis Symbols and Structures as well as Hybrid Atomic Orbitals.

5 Must Know Facts For Your Next Test

1. The trigonal pyramidal molecular geometry is characterized by a central atom bonded to three atoms and one lone pair of electrons.
2. This geometry is a result of the Valence Shell Electron Pair Repulsion (VSEPR) theory, which states that electron pairs around a central atom will arrange themselves to minimize repulsion.
3. Molecules with a trigonal pyramidal geometry have a bond angle of approximately 107 degrees between the three bonded atoms.
4. The presence of the lone pair of electrons on the central atom causes the molecule to be non-planar and have a slightly distorted shape.
5. Trigonal pyramidal geometry is commonly observed in molecules such as ammonia (NH3) and phosphine (PH3).

Review Questions

• Explain how the trigonal pyramidal molecular geometry is determined according to the VSEPR theory.
  • The trigonal pyramidal geometry is determined by the VSEPR theory, which states that the electron pairs around a central atom will arrange themselves to minimize repulsion. In the case of a trigonal pyramidal molecule, the central atom is bonded to three atoms and has one lone pair of electrons. The lone pair of electrons occupies more space than the bonding pairs, causing the three bonded atoms to be arranged in a trigonal pyramidal shape with a bond angle of approximately 107 degrees to minimize the repulsion between the electron pairs.
• Describe the key features of the trigonal pyramidal molecular geometry and how it differs from other common molecular geometries.
  • The trigonal pyramidal molecular geometry is characterized by a central atom bonded to three atoms and one lone pair of electrons. This non-planar, pyramid-like shape is distinct from other common molecular geometries, such as the trigonal planar (three bonded atoms, no lone pairs) and the tetrahedral (four bonded atoms, no lone pairs). The presence of the lone pair of electrons on the central atom in the trigonal pyramidal geometry causes a slight distortion in the shape, resulting in a bond angle of approximately 107 degrees, rather than the 120 degrees seen in the trigonal planar geometry.
• Analyze how the trigonal pyramidal molecular geometry and the presence of lone pairs of electrons on the central atom can influence the physical and chemical properties of a molecule.
  • The trigonal pyramidal geometry and the presence of a lone pair of electrons on the central atom can significantly impact the physical and chemical properties of a molecule. The non-planar, distorted shape of the molecule can affect its polarity, as the lone pair of electrons creates an unequal distribution of electron density, leading to a dipole moment. This polarity can influence the molecule's intermolecular interactions, such as hydrogen bonding, and its solubility in polar or non-polar solvents. Additionally, the lone pair of electrons on the central atom can influence the molecule's reactivity, as the lone pair can participate in various chemical reactions or coordinate with other atoms or molecules.

Related terms

Molecular Geometry:

The three-dimensional arrangement of atoms in a molecule, determined by the number of bonding pairs and lone pairs of electrons around the central atom.

Lone Pair: A pair of valence electrons that is not involved in a covalent bond, but is still associated with the central atom.

Valence Shell Electron Pair Repulsion (VSEPR) Theory:

A model used to predict the geometry of molecules based on the arrangement of electron pairs around the central atom to minimize electron pair repulsion.