Question

Parent Compound \(\mathrm{PCl}_{5}\) is used as a parent compound to form many other compounds. Explain the theory of hybridization and determine the number of hybrid orbitals present in a molecule of \(\mathrm{PCl}_{5}\) .

Short answer

Hybridization is a process that combines atomic orbitals to form a new set of equivalent hybrid orbitals, which are essential for understanding the geometry and bonding in molecules. In the \(\mathrm{PCl}_{5}\) molecule, the central atom Phosphorus has the electron configuration \[1s^2 \ 2s^2 \ 2p^6 \ 3s^2 \ 3p^3\]. To form \(\mathrm{PCl}_{5}\), Phosphorus needs to bond with 5 Chlorine atoms; thus, it requires 5 hybrid orbitals. Phosphorus promotes one of its 3s electrons to an empty 3d orbital and undergoes \(\mathrm{sp^3d}\) hybridization, involving one 3s, three 3p, and one 3d orbitals. As a result, the number of hybrid orbitals present in a molecule of \(\mathrm{PCl}_{5}\) is 5.

Step-by-step solution

Explain hybridization

Hybridization is a process that combines a set of atomic orbitals into a new set of equivalent hybrid orbitals. This concept is used to describe the geometry and bonding in molecules. The orbitals that participate in this process are called atomic orbitals, which include s, p, and sometimes d orbitals. In hybridization, these atomic orbitals mix and redistribute their energies and shapes to form hybrid orbitals that participate in bonding with other atoms.

Determine the electron configuration of the central atom

In the case of \(\mathrm{PCl}_{5}\), the central atom is Phosphorus (P). To understand the hybridization process, we need to determine the electron configuration of Phosphorus. The atomic number of phosphorus is 15, so its electron configuration is: \[1s^2 \ 2s^2 \ 2p^6 \ 3s^2 \ 3p^3\]

Analyze the valence electrons and orbitals for bonding

The valence shell of Phosphorus (in its ground state) has 5 electrons: 2 in the 3s orbital, and 3 in the 3p orbitals. To form \(\mathrm{PCl}_{5}\), Phosphorus needs to bond with 5 Chlorine atoms. As a result, there must be 5 hybrid orbitals available for bonding. To accommodate 5 hybrid orbitals, Phosphorus needs to promote one of its 3s electrons to an empty 3d orbital.

Determine the hybridization of Phosphorus

Now that phosphorus has a total of 5 available orbitals (1 in 3s, 3 in 3p, and 1 in 3d) for bonding, the atom will undergo hybridization to form 5 equivalent hybrid orbitals. In this case, the hybridization of Phosphorus will be \(\mathrm{sp^3d}\) since it involves one 3s, three 3p, and one 3d orbitals.

Determine the number of hybrid orbitals

As explained in Step 4, the hybridization of Phosphorus in the \(\mathrm{PCl}_{5}\) molecule is \(\mathrm{sp^3d}\). This means it forms a total of 5 hybrid orbitals. Therefore, the number of hybrid orbitals present in a molecule of \(\mathrm{PCl}_{5}\) is 5.

Key concepts

Electron Configuration

Electron configuration is a way to represent how electrons are arranged in an atom. It's important because it helps us understand the chemical properties of elements. For phosphorus, which is the central atom in \(\mathrm{PCl}_{5}\), the electron configuration is \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^3\). This means phosphorus has a total of 15 electrons distributed across different shells and subshells.
This configuration shows us that the outermost shell, or valence shell, has three electrons in the 3p subshell and two in the 3s subshell. These are the valence electrons, which are crucial for bonding. In \(\mathrm{PCl}_{5}\), phosphorus uses its outer shell electrons to form bonds with five chlorine atoms. Understanding electron configurations can also help us predict how atoms will bond and the geometry of the resulting molecules.

Valence Electrons

Valence electrons are electrons found in the outermost shell of an atom. They are significant because they participate in chemical bonding. For phosphorus in \( \mathrm{PCl}_{5} \), there are five valence electrons: two are in the 3s subshell, and three are in the 3p subshell.
These electrons are distributed in a way that allows phosphorus to form five bonds with chlorine atoms. This process involves hybridization, where phosphorus "promotes" one of its 3s electrons to an empty 3d orbital. This promotion gives phosphorus five equivalents orbitals to use in bonding, resulting in the hybridization form called \(\mathrm{sp^3d}\), and explaining how phosphorus can have five bonds in \( \mathrm{PCl}_{5} \).

• Two electrons in the 3s subshell
• Three electrons in the 3p subshell

Remember, valence electrons determine how atoms interact with each other.

Molecular Geometry

Molecular geometry refers to the three-dimensional shape of a molecule. This shape is crucial because it influences the molecule's properties and reactions. For the compound \(\mathrm{PCl}_{5}\), understanding its molecular geometry helps us predict how it behaves chemically and physically.
The hybridization of phosphorus to \(\mathrm{sp^3d}\) orbitals allows it to form five bonds. These are arranged in a trigonal bipyramidal geometry. In this shape, three chlorine atoms form a plane around the phosphorus atom, while the other two chlorine atoms occupy positions above and below this plane. The shape ensures minimal repulsion between the electron pairs.

• Trigonally planar base
• Two axial bonds above and below plane

Understanding molecular geometry offers insights into the reactivity and polarity of a molecule.

Phosphorus Compounds

Phosphorus compounds, like \(\mathrm{PCl}_{5}\), play a vital role in chemistry. Phosphorus is a versatile element capable of forming multiple bonds due to its ability to hybridize. This capability leads to the formation of various compounds with different properties and uses.
\(\mathrm{PCl}_{5}\) itself is used in various applications, like in the synthesis of other phosphorus-containing compounds. The ability of phosphorus to engage in \(\mathrm{sp^3d}\) hybridization makes it unique among the elements of its group, allowing the formation of five bonds. This hybridization stems from its specific electron configuration, which leads to the creation of distinct molecules.
Compounds involving phosphorus can range from simple molecular structures like phosphine to more complex structures like DNA. This versatility is primarily due to phosphorus's chemistry and bonding patterns.