Question

Carbon and silicon belong to Group \(4 \mathrm{~A}\) of the periodic table and have the same valence electron configuration \(\left(n s^{2} n p^{2}\right) .\) Why does silicon dioxide \(\left(\mathrm{SiO}_{2}\right)\) have a much higher melting point than carbon dioxide \(\left(\mathrm{CO}_{2}\right) ?\)

Short answer

SiO₂ has a higher melting point due to its strong network covalent structure, unlike the molecular structure of CO₂.

Step-by-step solution

Understand the Structure of Silicon Dioxide

Silicon dioxide \((\mathrm{SiO}_2)\) has a network covalent structure, meaning it forms a continuous 3D lattice of silicon and oxygen atoms. Each silicon atom forms four covalent bonds with oxygen in a tetrahedral arrangement, leading to a very stable and strong structure.

Analyze the Structure of Carbon Dioxide

Carbon dioxide \((\mathrm{CO}_2)\) is a simple molecular compound where each carbon atom forms double bonds with two oxygen atoms, resulting in a linear molecule. This structure leads to weak intermolecular forces (Van der Waals forces) between the molecules.

Compare Intermolecular Forces

In \(\mathrm{SiO}_2\), the strong covalent bonds extend throughout the lattice, making it difficult to break and requiring a lot of energy to do so. In contrast, \(\mathrm{CO}_2\) has weaker intermolecular forces, which are much easier to overcome, thus requiring less energy to melt.

Examine Melting Points

Due to the extensive covalent bonding in the \(\mathrm{SiO}_2\) network, it has a very high melting point. \(\mathrm{CO}_2\) sublimes at a much lower temperature because the energy required to transition from solid to gas is smaller due to its simple molecular structure.

Key concepts

Silicon Dioxide

Silicon dioxide, also known as silica, is a fascinating substance found in a variety of materials like sand and quartz. It has a network covalent structure, which means the atoms are arranged in a three-dimensional lattice. Each silicon atom is surrounded by four oxygen atoms, bonded in a stable tetrahedral shape. These strong bonds create a very rigid structure.

Since the entire solid is bonded together by these covalent bonds, a lot of energy is required to disrupt the lattice. This is why silicon dioxide can withstand very high temperatures and has a high melting point. The steadfast nature of these bonds gives ef SiO_2 ef its exceptional qualities in both durability and melting resistance.

Carbon Dioxide

Carbon dioxide is quite different from silicon dioxide, despite both containing oxygen. In the carbon dioxide molecule ef CO_2 ef, the structure is much simpler. Here, each carbon atom is double bonded to two oxygen atoms in a linear arrangement. This simple molecular structure means that the molecules are distinct, having less energy holding them together as a group.

The forces acting between ef CO_2 ef molecules are weak intermolecular forces, specifically the Van der Waals forces. Because these forces require little energy to break, carbon dioxide doesn't need a lot of heat to change its phase, leading to its much lower melting and sublimation point compared to ef SiO_2 ef.

Intermolecular Forces

Intermolecular forces are the forces that act between individual molecules. They are different from the covalent or ionic bonds that hold atoms together within a molecule. These forces influence the physical properties of substances, such as boiling and melting points.

There are various types of intermolecular forces, including:

• Van der Waals forces (dispersion forces)
• Dipole-dipole interactions
• Hydrogen bonds

In silicon dioxide, covalent bonds create an extensive network, requiring significant energy to break. In contrast, carbon dioxide's molecules are held together by Van der Waals forces, which require comparatively minimal energy to overcome.

This difference in the intermolecular forces explains the varying physical characteristics between these two molecules, particularly their melting and boiling points.

Melting Point

The melting point of a substance is a key physical property. It is the temperature at which a solid turns into a liquid. This property is heavily influenced by the strength of forces holding the particles together within the material.

Silicon dioxide, with its network covalent bonds, possesses a significantly high melting point. The extensive bonds must be broken to change its state, requiring substantial energy. On the other hand, carbon dioxide has a low melting point because it's made of simple molecular units held together by weak intermolecular forces. These forces are easily overcome, allowing ef CO_2 ef to sublime (change from solid to gas) at a relatively low temperature.

Understanding the melting point helps in comprehending why materials behave in certain ways when subjected to heat, emphasizing the role of molecular structure and bonding nature.