Problem 6 - Chemistry: The Central Science

Question

The orbital diagram that follows presents the final step in the formation of hybrid orbitals by a silicon atom. (a) Which of the following best describes what took place before the step pictured in the diagram: (i) Two 3 p electrons became unpaired, (ii) An electron was promoted from the \(2 p\) orbital to the \(3 s\) orbital, or (iii) An electron was promoted from the \(3 s\) orbital to the \(3 p\) orbital? (b) What type of hybrid orbital is produced in this hybridization? [Section 9.5]

Step-by-Step Solution

Answer

(a) The correct statement is (iii) An electron was promoted from the \(3s\) orbital to the \(3p\) orbital. (b) The type of hybrid orbital produced in this hybridization is sp3.

Step 1: Analyze the given orbital diagram of a silicon atom

To correctly answer the question, we need a clear understanding of the electronic configuration of a silicon atom. Silicon has 14 electrons, with the electron configuration as follows: \(1s^2, 2s^2, 2p^6, 3s^2, 3p^2\).

Step 2: Determine which statement best describes the process that took place

Now, we must identify which statement best describes what took place before the step pictured in the orbital diagram. (i) Two 3 p electrons became unpaired. (ii) An electron was promoted from the \(2 p\) orbital to the \(3 s\) orbital. (iii) An electron was promoted from the \(3 s\) orbital to the \(3 p\) orbital. Since Silicon has two electrons in the \(3s\) orbital and two electrons in the \(3p\) orbital, the most likely process to have occurred is (iii) An electron was promoted from the \(3s\) orbital to the \(3p\) orbital.

Step 3: Identify the type of hybrid orbital produced in this hybridization

To determine the type of hybrid orbital, we must analyze the number of orbitals that were involved in the hybridization process. In this case, we have: - One \(3s\) orbital - Three \(3p\) orbitals Together, the \(3s\) and \(3p\) orbitals form 4 hybrid orbitals. Since there are four orbitals involved, the hybridization process results in the formation of four new hybrid orbitals, which are called sp3 hybrid orbitals. So, the type of hybrid orbital produced in this hybridization is sp3. In conclusion: (a) The statement that best describes what took place before the step in the orbital diagram is (iii) An electron was promoted from the \(3s\) orbital to the \(3p\) orbital. (b) The type of hybrid orbital produced in this hybridization is sp3.

Key Concepts

SP3 Hybrid Orbitals

Hybridization is an essential concept in chemistry involving the mixing of atomic orbitals to form new hybrid orbitals. These new hybrid orbitals have different shapes and energies compared to their original atomic orbitals. One of the most common types of hybridization involves the combination of one s orbital and three p orbitals, leading to the formation of four equivalent sp3 hybrid orbitals.

Each sp3 hybrid orbital has an equal amount of s and p character, which is to say they are one-quarter s and three-quarters p. The geometry that results from sp3 hybridization is a tetrahedral arrangement, with each hybrid orbital pointing to the corners of a tetrahedron. This geometry is significant for molecules and ions because it helps explain the observed bonding angles of approximately 109.5 degrees in compounds such as methane (CH4).

In the context of a silicon atom, sp3 hybridization allows for the formation of silicon-centered compounds with four equivalent Si-C bonds, as seen in silicone polymers or the silicones in various industrial applications.

Electronic Configuration

Understanding the electronic configuration of atoms is crucial to predict their chemical behavior. The electronic configuration of an atom depicts how its electrons are distributed among various atomic orbitals. In the case of silicon with an atomic number of 14, its ground-state electron configuration is given by the following sequence of filled orbitals:

1. 1s²
2. 2s²
3. 2p⁶
4. 3s²
5. 3p²

The 1s, 2s, and 2p orbitals are fully filled, while the 3s and 3p orbitals are partially filled with two electrons each. It's the electrons in these outermost orbitals that can engage in the hybridization process to enable chemical bonding.

For instance, when forming sp3 hybrid orbitals in a silicon atom, one of the electrons in the 3s orbital is excited to a higher 3p orbital. This allows the atom to have four unpaired electrons, which can then overlap with orbitals from other atoms to form bonds. The concept of electronic configuration determines not only the hybridization state but also the valency and the type of bonds an atom can form.

Silicon Atom Hybridization

When discussing the hybridization of a silicon atom, we consider how the atom reorganizes its electrons to accommodate bonding with other elements. Silicon, located in group 14 of the periodic table, primarily undergoes sp3 hybridization when it forms four covalent bonds with other atoms. This hybridization is analogous to that of carbon, the element just above silicon on the table.

The process involves raising one of its 3s electrons to an empty or half-filled 3p orbital, which requires energy input. By promoting an electron, silicon now has four unpaired electrons, each occupying separate orbitals. These four atomic orbitals then hybridize to form four new equivalent sp3 hybrid orbitals that are degenerate—that is, they all have the same energy level.

Consequently, a silicon atom can form tetrahedral structures in compounds like silicon dioxide (SiO2) and various silicates that make up a significant portion of the earth's crust. The versatility of sp3 hybrid orbitals in silicon enables it to form stable bonds with a variety of elements, playing a vital role in materials ranging from semiconductors to biomedical implants.