1. Bonding:
* Methane: Methane has covalent bonds between carbon and hydrogen atoms. These bonds are relatively weak and are easily broken.
* Silicon dioxide: Silicon dioxide forms a network covalent structure. Silicon and oxygen atoms are linked together in a giant three-dimensional network with strong covalent bonds throughout. This network structure is very strong and requires a lot of energy to break.
2. Intermolecular forces:
* Methane: Methane molecules are held together by weak London dispersion forces, which are the weakest type of intermolecular forces. These forces are easily overcome by thermal energy.
* Silicon dioxide: Due to the strong network covalent structure, the intermolecular forces in silicon dioxide are essentially intramolecular forces within the network. This leads to very strong attractions between atoms, requiring much higher energy to overcome.
3. Molecular size and complexity:
* Methane: Methane is a small, simple molecule with only one carbon atom.
* Silicon dioxide: Silicon dioxide has a complex network structure with a high degree of interconnectivity. This larger and more complex structure leads to a higher melting point.
In summary:
The strong network covalent bonds in silicon dioxide, coupled with its complex structure, lead to much higher melting points compared to the weak covalent bonds and weak intermolecular forces in methane. This is why silicon dioxide melts at around 1713 °C, while methane melts at -182.5 °C.
