Question

Besides the central atom, what are the differences between \(\mathrm{CO}_{2}\) and \(\mathrm{SiO}_{2}\) ?

Short answer

The main differences between \(\mathrm{CO}_{2}\) and \(\mathrm{SiO}_{2}\) molecules, besides the central atom, are their chemical composition, molecular structure, and properties. \(\mathrm{CO}_{2}\) has a linear, non-polar structure and is a gas at room temperature, whereas \(\mathrm{SiO}_{2}\) forms a polar, tetrahedral crystalline solid called quartz. Moreover, \(\mathrm{CO}_{2}\) has much lower melting and boiling points compared to \(\mathrm{SiO}_{2}\) due to the absence of strong covalent bonds in its structure.

Step-by-step solution

Identify the Central Atoms

In the given molecules, the central atoms are Carbon (C) in \(\mathrm{CO}_{2}\) and Silicon (Si) in \(\mathrm{SiO}_{2}\).

Examine the Chemical Composition

Both molecules have one central atom and two oxygen atoms. However, the \(\mathrm{CO}_{2}\) molecule is composed of one carbon atom and two oxygen atoms, while the \(\mathrm{SiO}_{2}\) molecule consists of one silicon atom and two oxygen atoms.

Investigate the Molecular Structure

The \(\mathrm{CO}_{2}\) molecule has a linear structure, with the carbon atom at the center and oxygen atoms on either side. The bond angle between the carbon and oxygen atoms is 180°. The molecule is non-polar because the positive and negative charges are symmetrically distributed. On the other hand, the \(\mathrm{SiO}_{2}\) molecule has a different structure. Silicon dioxide exists mainly in the form of a three-dimensional network called a tetrahedral structure. Each silicon atom is bonded to four oxygen atoms, while each oxygen atom is bonded to two silicon atoms. As a result, the molecule forms a crystalline solid known as quartz, which is a very stable and highly abundant compound.

Compare the Properties

The differences in structure between the two molecules lead to variations in their properties. Some of the main differences are: 1. Physical State: \(\mathrm{CO}_{2}\) is a gas at room temperature, whereas \(\mathrm{SiO}_{2}\) is a crystalline solid. 2. Polarity: \(\mathrm{CO}_{2}\) is a non-polar molecule, while \(\mathrm{SiO}_{2}\) is polar due to the difference in electronegativity between silicon and oxygen atoms. 3. Melting and Boiling Points: \(\mathrm{CO}_{2}\) has much lower melting and boiling points compared to \(\mathrm{SiO}_{2}\) due to the absence of strong covalent bonds in its structure. In summary, the main differences between the \(\mathrm{CO}_{2}\) and \(\mathrm{SiO}_{2}\) molecules, besides the central atom, are their chemical composition, molecular structure, and various properties related to the differences in structure.

Key concepts

Chemical Composition

Understanding the chemical composition of molecules is fundamental to grasp how different substances behave. Chemical composition refers to the identity and ratio of the atoms that constitute a chemical compound. In the case of CO2 and SiO2, both molecules incorporate the same types of atoms—carbon or silicon and oxygen. Nevertheless, they differ in how these atoms are arranged and bonded.

While CO2 is made up of one carbon atom doubly bonded to two oxygen atoms, SiO2 features a silicon atom that forms single bonds with four oxygen atoms. This distinct arrangement leads to remarkably different physical and chemical properties, such as hardness, melting point, and reactivity.

The way these elements are connected can also influence the reactivity and interactions of the molecules with other substances. For instance, the linear structure of CO2 renders it quite inert, whereas the tetrahedral structure of SiO2 contributes to its high stability and ability to form extended networks.

Physical State of Compounds

The physical state of a compound at a given temperature and pressure is an important characteristic often determined by its molecular structure. CO2 is a gas at room temperature, allowing its molecules to move freely and independently. This is due to the non-polar nature of the CO2 molecule, which results in weak intermolecular forces such as dispersion forces.

Conversely, SiO2 exists as a crystalline solid. Its extended tetrahedral network creates a strong, interconnected lattice that requires significant energy to break, thus conferring high melting and boiling points. The structural attributes of each compound fundamentally influence whether it will be a solid, liquid, or gas under certain conditions, with implications for its usage in various applications.

For example, the gaseous nature of CO2 makes it suitable for use in fire extinguishers and refrigeration, while the solid structure of SiO2 lends itself to applications in construction and electronics as quartz or silica.

Molecular Polarity

Polarity is a concept that describes the distribution of electrical charge over the atoms joined by a bond or over the entire molecule. Molecular polarity influences solubility, boiling and melting points, and the types of chemical reactions a molecule can participate in.

In CO2, the molecule is linear with a symmetrical charge distribution, making it non-polar. This symmetry means that the opposite charges cancel out, leading to a lack of permanent dipole. As a result, CO2 does not readily dissolve in water and has lower boiling and melting points compared to polar compounds.

On the other hand, the SiO2 molecule is polar, arising from the difference in electronegativity between the silicon and oxygen atoms. The geometry of the molecule isn't symmetrical across all planes, and does not cancel out the dipoles, leading to regions of partial positive and negative charge. This polarity allows SiO2 to engage in stronger intermolecular forces like hydrogen bonding, contributing to its high melting and boiling points and its solidity at room temperature.