Phosphorus pentachloride (PCl5)

Definition

Phosphorus pentachloride is a chemical compound consisting of one phosphorus atom and five chlorine atoms. This compound is notable for its unique molecular structure and its role in various chemical reactions, particularly in the context of understanding molecular geometry and bond angles as described by VSEPR theory.

5 Must Know Facts For Your Next Test

1. Phosphorus pentachloride has a trigonal bipyramidal molecular geometry, which is derived from VSEPR theory, indicating that it has bond angles of 120° and 90° around the phosphorus atom.
2. In phosphorus pentachloride, the phosphorus atom utilizes its empty d-orbitals to accommodate the five chlorine atoms, leading to its unique bonding characteristics.
3. PCl5 can exist in two forms: a solid at room temperature and a gas when heated, demonstrating different physical states that are dependent on temperature.
4. This compound is used as a chlorinating agent in organic synthesis, highlighting its importance in various chemical reactions and processes.
5. Phosphorus pentachloride can react with water to produce phosphorus oxychloride and hydrochloric acid, showcasing its reactivity with moisture.

Review Questions

• How does VSEPR theory explain the molecular geometry of phosphorus pentachloride?
  • VSEPR theory explains that phosphorus pentachloride has a trigonal bipyramidal geometry due to the arrangement of five electron pairs around the central phosphorus atom. The repulsion between these electron pairs leads to specific bond angles of 120° in the equatorial plane and 90° between the axial and equatorial positions. This geometric arrangement minimizes repulsion, resulting in a stable structure for PCl5.
• Compare the bonding characteristics of phosphorus pentachloride with another similar halogenated compound.
  • When comparing phosphorus pentachloride to sulfur dichloride (SCl2), we see distinct differences in bonding and geometry. While PCl5 has a trigonal bipyramidal shape due to five bonds, SCl2 features a bent structure due to its two bonded chlorine atoms and two lone pairs on sulfur. This contrast highlights how central atom hybridization and lone pair presence influence molecular shapes and reactivity in halogenated compounds.
• Evaluate the significance of phosphorus pentachloride's reactivity with water in terms of its practical applications in chemistry.
  • The reactivity of phosphorus pentachloride with water is significant because it illustrates PCl5's role as a chlorinating agent in organic synthesis. When it reacts with water, it produces phosphorus oxychloride and hydrochloric acid, which can be useful in various chemical processes. This reaction underscores how understanding PCl5's behavior enhances our ability to manipulate chemical reactions for desired outcomes, especially in synthetic organic chemistry.

Related terms

VSEPR Theory: A model used to predict the geometry of individual molecules based on the repulsion between the electron pairs surrounding their central atom.

Molecular Geometry: The three-dimensional arrangement of atoms in a molecule, which can influence the physical and chemical properties of the substance.

Chlorine: A highly reactive greenish-yellow gas that is a member of the halogen group and is used in various chemical processes.