Question

(a) What is the characteristic geometry about silicon in all silicate minerals? (b) Metasilicic acid has the empirical formula \(\mathrm{H}_{2} \mathrm{SiO}_{3}\). Which of the structures shown in Figure \(22.46\) would you expect metasilicic acid to have?

Short answer

(a) The characteristic geometry of silicon in all silicate minerals is a tetrahedral arrangement, known as the silicon-oxygen tetrahedron. (b) To determine the structure of metasilicic acid, examine Figure 22.46 and look for a structure with a tetrahedral arrangement of silicon and oxygen atoms, two oxygen atoms attached to a hydrogen atom each, and an overall formula of \(\mathrm{H}_{2}\mathrm{SiO}_{3}\). The structure that meets these criteria is the expected structure for metasilicic acid.

Step-by-step solution

Part (a): Identifying the Characteristic Geometry

Silicon is a group IV element with four valence electrons. In silicate minerals, silicon forms bonds with oxygen, creating a tetrahedral structure. This tetrahedral structure is known as the silicon-oxygen tetrahedron. In the silicon-oxygen tetrahedron, silicon is at the center and is surrounded by four oxygen atoms located at the vertices. Each oxygen atom is bonded to the silicon atom through a single covalent bond. So, the characteristic geometry of silicon in all silicate minerals is a tetrahedral arrangement.

Part (b): Analyzing the Metasilicic Acid Formula and Figure 22.46

The empirical formula of metasilicic acid is \(\mathrm{H}_{2}\mathrm{SiO}_{3}\). This formula shows that we have one silicon atom, two hydrogen atoms, and three oxygen atoms. To determine the structure of metasilicic acid, we need to analyze the structures given in Figure 22.46. Note: As the actual Figure 22.46 is not provided here, we will assume it contains a few structures involving the silicon-oxygen tetrahedron. We should look for a structure in Figure 22.46 that meets the following requirements: 1) The structure incorporates the tetrahedral arrangement of silicon and oxygen atoms. 2) Two of the oxygen atoms within the structure are attached to a hydrogen atom each. 3) The overall formula of the structure gives the empirical formula \(\mathrm{H}_{2}\mathrm{SiO}_{3}\). By examining Figure 22.46, identify the structure that fulfills the requirements mentioned above. The structure that meets these criteria would be the expected structure for metasilicic acid.

Key concepts

Silicon-Oxygen Tetrahedron

The silicon-oxygen tetrahedron is a fundamental building block in the world of silicate minerals. Imagine the shape of a pyramid with a triangular base, and a silicon atom sitting snugly at its center. This is what a silicon-oxygen tetrahedron looks like. Each of the four corners, or vertices, of this tetrahedron is occupied by an oxygen atom. These oxygen atoms are linked to the central silicon atom through covalent bonds. This arrangement repeats itself in many structures, making it the backbone for a plethora of silicate minerals.

• The central silicon atom is surrounded symmetrically by the four oxygen atoms.
• Each silicon-oxygen bond is strong and stable.
• This tetrahedral shape allows for extensive linking in mineral structures.

In silicate minerals, these tetrahedrons can link together to form diverse and complex structures. They can form single units, or join in chains, sheets, or three-dimensional frameworks. This versatility contributes to the wide variety of mineral properties and appearances found in nature.

Metasilicic Acid

Metasilicic acid, with the empirical formula \(\text{H}_2\text{SiO}_3\), is a representation of a specific arrangement of silicon, oxygen, and hydrogen. Understanding its structure relies on envisioning how the components of the silicon-oxygen tetrahedron fit within the molecule and adhere to its formula.
For metasilicic acid:

• There is one silicon atom, which characterizes its tetrahedral backbone.
• The three oxygen atoms are part of this tetrahedral assembly and dictate the connectivity within the molecule.
• Two hydrogen atoms are attached to two separate oxygen atoms, ensuring the molecular formula is correct.

The structure of metasilicic acid can often be found represented in diagrams similar to "Figure 22.46" mentioned in exercises. These diagrams are essential as they visually confirm whether a theoretical construction aligns with its simplest formula.

Empirical Formula

The empirical formula gives us a simplified way to represent chemical compositions. It shows the simplest ratio of the elements within a compound. For example, in the case of metasilicic acid, \(\text{H}_2\text{SiO}_3\), the formula tells us that the elements hydrogen, silicon, and oxygen are present in a 2:1:3 ratio, respectively.
Understanding empirical formulas is crucial because:

• It provides a basic chemical identity for a substance without detailing its structure.
• This simplification is useful for identifying the relative proportion of elements.
• Even when molecular structure is complex, empirical formulas help in early predictions and analysis.

It's important to note that empirical formulas don't always inform about the exact molecular structure or arrangement of atoms. It's a starting point for understanding chemical composition and helps in determining the stoichiometry of reactions.