key term - Trigonal planar geometry

Definition

Trigonal planar geometry refers to a molecular shape where three atoms are bonded to a central atom, forming a flat, triangular arrangement. This geometry is commonly associated with molecules that have a steric number of 3, resulting from the combination of one central atom and three bonded atoms, with no lone pairs of electrons influencing the shape.

5 Must Know Facts For Your Next Test

1. Trigonal planar geometry features bond angles of approximately 120 degrees due to the equal repulsion among the three bonding pairs of electrons.
2. Common examples of molecules with trigonal planar geometry include boron trifluoride (BF3) and formaldehyde (CH2O).
3. The trigonal planar shape arises from sp2 hybridization, where one s orbital mixes with two p orbitals to create three equivalent hybrid orbitals.
4. In trigonal planar geometry, there are no lone pairs on the central atom; if lone pairs are present, they can alter the geometry to a bent shape.
5. Understanding trigonal planar geometry is crucial for predicting the reactivity and physical properties of certain molecules in organic and inorganic chemistry.

Review Questions

• How does the concept of steric number help explain the formation of trigonal planar geometry in molecules?
  • The steric number is essential in determining molecular shapes, including trigonal planar geometry. A steric number of 3 indicates that there are three bonded atoms around a central atom and no lone pairs. This arrangement leads to a planar structure, as the electron pairs maximize their distance from each other, resulting in bond angles close to 120 degrees.
• Discuss how hybridization plays a role in achieving trigonal planar geometry, particularly focusing on sp2 hybridization.
  • Hybridization is key to understanding how trigonal planar geometry arises in molecules. In sp2 hybridization, one s orbital and two p orbitals combine to form three equivalent sp2 hybrid orbitals. These orbitals arrange themselves in a trigonal planar shape around the central atom, ensuring that the three bonds formed have equal bond angles of approximately 120 degrees, which minimizes electron pair repulsion.
• Evaluate the significance of VSEPR theory in predicting trigonal planar geometry and its implications for molecular behavior.
  • VSEPR theory is vital for predicting molecular geometries such as trigonal planar arrangements. It explains how electron pair repulsion leads to specific shapes by considering both bonding and lone electron pairs. By applying VSEPR theory, chemists can anticipate how molecules will interact with each other based on their geometries, which has implications for reactivity, polarity, and even biological activity in various chemical contexts.

Related terms

Steric Number: The steric number is the total number of electron pairs (bonding and lone pairs) surrounding a central atom, which helps determine the molecular geometry.

Hybridization:

Hybridization is the mixing of atomic orbitals to form new hybrid orbitals, which dictate the bonding and geometry of molecules.

VSEPR Theory: Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the 3D shapes of molecules based on the repulsion between electron pairs around a central atom.