Structure
Silicon Dioxide is a 3-D network solid,
with a tetrahedral arrangement. Each silicon atom is bonded to
four oxygen atoms, and each oxygen atom is bonded to two
silicons. This structure is also referred to as a macromolecule
due to the covalent bonds.
Sulfur Dioxide is a molecular solid, made of sulfur dioxide molecules which are covalently bonded with one lone pair which makes it a bent shape. However, the solid is held together with dipole-dipole force due to its polarity.
Silicon Dioxide
Sulfur Dioxide
Bonding
Covalent Bonds hold both SiO2 and SO2 molecules together. Since SO2 is a molecular solid, it is held together by intermolecular forces such as the Dipole-Dipole force because it is a polar molecule. SiO2 is only held by covalent bonds which is why it is a network solid.
Properties
Melting Point
SiO2
1,713 °C
SO2
−72 °C
Electrical Conductivity
SiO2
None
SO2
None(solid) / Low(in water)
Solubility in Water
SiO2
Insoluble
SO2
Soluble
SiO2 has a high melting point due to the covalent bonds holding it together.
SO2 has a low melting point because it is held together with intermolecular forces.
The electrons in both are bound in the covalent bond, which means they are not free to move. Therefore making both unable to conduct electricity.
Since Sulfur Dioxide is soluble in water, when Sulfur Dioxide reacts with water it forms ions which can conduct electricity.
SiO2 is not soluble because the bonds are not polar, which means they cannot react with polar water molecules.
SO2 has polar bonds which makes it soluble in water.
Factors
The intramolecular forces holding SiO2 together as a solid are much stronger than the intermolecular forces holding SO2 together, therefore making SiO2 have a higher melting point.