Chapter 2: Problem 13

Why does quartz have no additional cations (other than \(\mathrm{Si}^{+4}\) )?

Short Answer

Expert verified

Quartz has the chemical formula \(\mathrm{SiO_2}\), where each silicon (\(\mathrm{Si}\)) atom forms covalent bonds with two oxygen (\(\mathrm{O}\)) atoms, creating a stable and electrically neutral crystal structure. The structure of quartz is built up by a continuous network of tetrahedral units with a central silicon atom and four surrounding oxygen atoms. The silicon atom has a charge of \(\mathrm{Si}^{+4}\), which balances with the negative charges from the oxygen atoms. Introducing any additional cation would disrupt the charge balance and negatively affect the structural stability of quartz. Therefore, quartz has no additional cations other than \(\mathrm{Si}^{+4}\).

Step by step solution

Understanding the basic formula of quartz

Quartz is a common mineral with the chemical formula \(\mathrm{SiO_2}\). In this compound, each silicon atom (\(\mathrm{Si}\)) forms covalent bonds with two oxygen atoms (\(\mathrm{O}\)), and each oxygen atom bonds with two silicon atoms. This means, in the most basic structure of quartz, we have one Si atom and two O atoms, bonded together and forming a repeating unit throughout the crystal structure.

Understanding the structure of quartz

The structure of quartz is built up by a continuous network of tetrahedra, where each silicon atom is surrounded by four oxygen atoms. This structure, called a silica tetrahedron, has a central silicon atom that forms four single covalent bonds with oxygen atoms. These tetrahedra are linked together in various ways, which is the basis for the many different types of silicates, including quartz.

Silicon cations in quartz

In quartz, the silicon atom has a charge of \(\mathrm{Si}^{+4}\) because it has lost four electrons to form covalent bonds with the surrounding oxygen atoms. This charge on the silicon atom creates a uniformly charged, stable structure. The silicon atom occupies the vertices of the silica tetrahedron, and oxygen atoms are located at the center of the faces.

No additional cations needed in quartz

The quartz structure relies on the stable bond between silicon and oxygen atoms. The \(\mathrm{SiO_2}\) structure is neutral in charge because the positive charge of \(\mathrm{Si}^{+4}\) balances with the negative charges from two oxygen atoms. Introducing any additional cation would disrupt the charge balance and negatively affect the structural stability of quartz. Since the arrangements of silicon and oxygen atoms in the crystal lattice create a stable and electrically neutral structure, there is no need for any additional cations to be introduced into the quartz structure.

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Why does quartz have no additional cations (other than \(\mathrm{Si}^{+4}\) )?

Short Answer

Step by step solution

Understanding the basic formula of quartz

Understanding the structure of quartz

Silicon cations in quartz

No additional cations needed in quartz

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