Determine the molecular geometry and sketch each molecule or ion using the bond conventions shown in “Representing Molecular Geometries on Paper” in Section 11.4. c. PCl5

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Determine the central atom: In PCl_5, phosphorus (P) is the central atom because it is less electronegative than chlorine (Cl) and can form more bonds.

Count the total number of valence electrons: Phosphorus has 5 valence electrons, and each chlorine has 7 valence electrons. Therefore, the total number of valence electrons is 5 + (5 * 7) = 40.

Draw the Lewis structure: Place phosphorus in the center and arrange the five chlorine atoms around it. Distribute the 40 valence electrons to form single bonds between phosphorus and each chlorine, using 10 electrons for the bonds and placing the remaining electrons as lone pairs on the chlorine atoms.

Determine the electron-pair geometry: With five bonding pairs and no lone pairs on the central atom, the electron-pair geometry is trigonal bipyramidal.

Determine the molecular geometry: Since there are no lone pairs on the central atom, the molecular geometry is also trigonal bipyramidal. Sketch the molecule with three chlorine atoms in the equatorial plane and two chlorine atoms in the axial positions.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. It is determined by the number of bonding pairs and lone pairs of electrons around the central atom, which influences the shape of the molecule. Common geometries include linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral.

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the geometry of molecules based on the repulsion between electron pairs in the valence shell of the central atom. According to VSEPR, electron pairs will arrange themselves to minimize repulsion, leading to specific molecular shapes. This theory is essential for determining the geometry of molecules like PCl5.

Bonding and Lone Pairs

In molecular structures, bonding pairs are the pairs of electrons shared between atoms, while lone pairs are the non-bonding pairs of electrons that belong to a single atom. The presence of lone pairs can significantly affect the molecular geometry by altering bond angles and overall shape. For PCl5, the arrangement of five bonding pairs around phosphorus leads to a trigonal bipyramidal geometry.

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