Question

(a) Determine the charge of the aluminosilicate ion whose composition is \(\mathrm{AlSi}_{3} \mathrm{O}_{10}\). (b) Using Figure \(22.33\), propose a reasonable description of the structure of this aluminosilicate.

Short answer

The charge of the aluminosilicate ion AlSi3O10 is -5 (AlSi3O10⁵⁻). Its structure is likely a framework of interconnected polyhedra with Si and Al atoms at the corners of tetrahedra and O atoms connecting them. The negative charge suggests covalent bonds between the oxygen and metals, as well as the presence of charge-balancing cations in the structure.

Step-by-step solution

Determine the charge of individual ions in the formula.

For AlSi3O10, we have the following ions: aluminum (Al), silicon (Si), and oxygen (O). We need to find the charge of each ion and use this information to find the total charge of the aluminosilicate ion. From the periodic table, we know that aluminum has a +3 charge (Al³⁺), silicon has a +4 charge (Si⁴⁺), and oxygen has a -2 charge (O²⁻).

Calculate the total charge of the aluminosilicate ion.

Now that we have the charge of each individual ion, we can determine the total charge of the aluminosilicate ion by multiplying the charge of each ion with its stoichiometric coefficient and summing up the charges. Total charge = (Charge of Al) + (Charge of Si x 3) + (Charge of O x 10) Total charge = (Al³⁺) + (Si⁴⁺ x 3) + (O²⁻ x 10) Total charge = +3 + (+4 x 3) + (-2 x 10) Total charge = +3 + 12 - 20 Total charge = -5 Therefore, the charge of the aluminosilicate ion AlSi3O10 is -5 (AlSi3O10⁵⁻).

Proposing the structure of the aluminosilicate ion.

We are asked to use Figure 22.33 to propose a reasonable description of the structure of the aluminosilicate ion. Since the figure is not provided, we cannot give a detailed description of the structure. However, we can make some general observations based on the composition: 1. The aluminosilicate ion has aluminum, silicon, and oxygen as its main constituents. 2. Since silicon and aluminum are found in the same group of the periodic table (Group 13), they might have similar coordination environments and bond with oxygen in a similar way. 3. Oxygen forms multiple bonds with silicon and aluminum, creating a framework structure. 4. The negative charge on the ion suggests that there will likely be covalent bonds between the oxygen and the metals, as well as possibly some charge-balancing cations in the structure. In general, aluminosilicates are part of a larger family of minerals known as tectosilicates, which often have a framework structure of interconnected polyhedra. Si and Al atoms are found at the corners of tetrahedra with O atoms connecting them, contributing to the overall negative charge of the aluminosilicate ion.

Key concepts

Ionic Charge Calculation

In ionic charge calculation, we decipher the overall electric charge of a compound by evaluating the charges of individual ions. The aluminosilicate ion AlSi3O10 is made up of aluminum (Al), silicon (Si), and oxygen (O). Each of these elements has a known charge: aluminum has a +3 charge (\(\text{Al}^{3+}\)), silicon a +4 charge (\(\text{Si}^{4+}\)), and oxygen typically carries a -2 charge (\(\text{O}^{2-}\)).
The total ionic charge is calculated by summing the individual charges, taking their stoichiometric coefficients into account:

• Charge from aluminum: \(+3\)
• Charge from silicon: \(+4 \times 3 = +12\)
• Charge from oxygen: \(-2 \times 10 = -20\)

Adding up these charges (\(+3 + 12 - 20\)), the total charge for AlSi3O10 results in \(-5\). This means the aluminosilicate ion carries a negative charge of \(-5\) (\(\text{AlSi}_3\text{O}_{10}^{5-}\)). This calculation is crucial for understanding the behavior and structure of compounds at the molecular level.

Silicon-Oxygen Tetrahedra

Silicon-oxygen tetrahedra form the basic building blocks of many silicate minerals. In these structures, a single silicon atom is surrounded by four oxygen atoms placed at the corners of a tetrahedron. This geometric arrangement is due to silicon's ability to form strong covalent bonds with oxygen.
In the aluminosilicate ion AlSi3O10, three silicon atoms each form their own tetrahedron by bonding with four oxygens. These tetrahedra are essential in defining the properties and structural complexity of silicate minerals.

• Each Si atom connects with four O atoms.
• The tetrahedral form is a stable and prevalent natural structure.
• The tetrahedra can link in various ways, creating diverse mineral structures.

Understanding these tetrahedral arrangements helps in appreciating how strong and durable aluminosilicate materials, like those in rocks and clays, are formed.

Tectosilicate Structure

Tectosilicates are minerals that contain a framework structure composed of interconnected tetrahedra. In the case of aluminosilicates, such as AlSi3O10, the tetrahedra share oxygen atoms, allowing them to form a vast, interconnected network. This framework contributes significantly to the stability and rigidity of silicate materials.
The sharing of oxygens in the tetrahedral network reduces the overall negative charge of the structure, which is crucial for achieving charge balance in minerals.

• Tetrahedra are linked in a network-like formation.
• Aluminum can replace silicon in some tetrahedra, influencing the framework's properties.
• These structures are found in various minerals, including quartz and feldspar.

This widespread framework structure provides the foundation for many geological formations and is essential to understand the behavior of silicate minerals under varying environmental conditions.

Aluminum Coordination

In aluminosilicate minerals, aluminum commonly coordinates with oxygen. While silicon is typically found in a tetrahedral coordination with oxygen, aluminum can sometimes occupy this same tetrahedral space, substituting silicon.
In AlSi3O10, there is one aluminum atom. Aluminum has slightly larger ionic radius than silicon, which can influence the structural and physical properties when it takes part in the tetrahedral framework.

• Aluminum can substitute for silicon in the tetrahedral structure.
• Its coordination affects the charge distribution and balance.
• This can lead to variations in mineral composition and properties.

Understanding aluminum coordination helps explain the mineralogical diversity within the aluminosilicate group, influencing both the mineral's stability and its uses in industry and nature.

Covalent Bonding in Silicates

Covalent bonding in silicates is a fundamental aspect of their stability and structural integrity. Silicon and oxygen atoms form robust covalent bonds, which are strong and directional. In aluminosilicates, these bonds contribute to creating resilient and stable frameworks. This bonding nature is one reason why silicate minerals are so durable and resistant to many forms of chemical and physical weathering, making them predominant in Earth's crust.

• Silicon and oxygen form strong covalent bonds.
• The resilience of silicates is due to these sturdy bonds.
• Such bonding allows for complex structures, enhancing mineral diversity.

Appreciating the covalent bonding mechanisms in silicates is essential for anyone interested in geology, materials science, or environmental science, as these determine many of their properties and behaviors.