Trigonal planar geometry

Definition

Trigonal planar geometry describes a molecular shape where three atoms are arranged around a central atom, forming a flat, triangular configuration with bond angles of approximately 120 degrees. This geometry is commonly observed in molecules with sp² hybridization, leading to a planar structure that minimizes electron pair repulsion according to VSEPR theory.

5 Must Know Facts For Your Next Test

1. Trigonal planar geometry typically occurs in molecules like BF₃ and C₂H₄, where the central atom is bonded to three other atoms without any lone pairs.
2. The bond angles in trigonal planar geometry are approximately 120 degrees due to the arrangement of electron pairs in a plane to minimize repulsion.
3. In the case of molecules with lone pairs, like SO₂, the geometry can be described as 'bent' rather than trigonal planar because lone pairs occupy more space and repel bonding pairs.
4. Trigonal planar geometry can also lead to variations in reactivity and properties of molecules due to its specific spatial arrangement.
5. Understanding trigonal planar geometry is essential for predicting molecular behavior in chemical reactions and interactions due to its influence on polarity and sterics.

Review Questions

• How does VSEPR theory explain the formation of trigonal planar geometry in molecules?
  • VSEPR theory explains trigonal planar geometry by considering the repulsion between electron pairs around a central atom. In this arrangement, three bonding pairs of electrons are distributed as far apart as possible in a single plane, resulting in bond angles of about 120 degrees. This minimizes electron-electron repulsion, leading to a stable, flat molecular shape characteristic of trigonal planar molecules.
• What role does sp² hybridization play in determining the geometry of a molecule, and how does it differ from other types of hybridization?
  • Sp² hybridization involves mixing one s orbital with two p orbitals to create three equivalent sp² hybrid orbitals, each oriented 120 degrees apart in a plane. This specific arrangement supports trigonal planar geometry. In contrast, sp³ hybridization leads to tetrahedral arrangements with bond angles of about 109.5 degrees, while sp hybridization results in linear geometries with bond angles of 180 degrees. Understanding these differences helps predict molecular shapes accurately.
• Evaluate how the presence of lone pairs affects the expected trigonal planar geometry of a molecule and provide an example.
  • The presence of lone pairs can significantly alter the expected trigonal planar geometry by introducing additional repulsion. For example, in sulfur dioxide (SO₂), although the central sulfur atom has three regions of electron density (two bonding pairs and one lone pair), the shape is bent rather than trigonal planar. This is due to the lone pair exerting greater repulsive force on adjacent bonding pairs, reducing the bond angle and creating a non-planar structure that reflects altered spatial arrangements.

Related terms

VSEPR theory: Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the geometry of individual molecules based on the repulsion between electron pairs surrounding the central atom.

sp² hybridization: Sp² hybridization occurs when one s orbital and two p orbitals mix to form three equivalent sp² hybrid orbitals, which are oriented 120 degrees apart in a plane, contributing to trigonal planar geometries.

bond angle: Bond angle refers to the angle formed between two bonds that share a common atom, which is crucial in determining the shape of a molecule.