For the following crystals, explain how their melting points are related to the bonding forces and the crystal structure.
Copper,Cu
Water,H2O
Sodium chloride,NaCl
Diamond,C
To understand how the melting points of crystals are related to bonding forces and crystal structure, let's examine each crystal individually.
1. Copper (Cu): Copper is a metal that forms a metallic crystal structure. In metallic bonding, the atoms are held together by a sea of delocalized electrons, which results in a strong bonding force. The melting point of copper is relatively high (approximately 1,085°C or 1,985°F) because metallic bonds are strong and require significant energy to break. Therefore, the strong bonding forces between copper atoms are responsible for its high melting point.
2. Water (H2O): Water is a molecular compound that forms a crystal lattice in the solid state. The crystal structure of ice, the solid form of water, consists of hydrogen bonds between water molecules. Hydrogen bonding occurs when a hydrogen atom, covalently bonded to an electronegative atom like oxygen, interacts with another electronegative atom. Hydrogen bonds are relatively strong intermolecular forces, but weaker than the metallic bonds mentioned earlier. Consequently, the melting point of water is relatively low (0°C or 32°F) compared to metals. This is because less energy is required to break the hydrogen bonds between water molecules.
3. Sodium chloride (NaCl): Sodium chloride, or common salt, forms an ionic crystal lattice. In an ionic compound, such as NaCl, the positively charged metal ions (sodium) are attracted to the negatively charged non-metal ions (chloride) through strong electrostatic forces. These ionic bonds are very strong, leading to a high melting point for sodium chloride (approximately 801°C or 1,474°F). Breaking these strong electrostatic forces requires a significant amount of energy, resulting in a high melting point.
4. Diamond (C): Diamond is a covalent crystal structure consisting of carbon atoms bonded together in a tetrahedral network. Covalent bonds are strong and occur when atoms share electrons. In the case of diamond, each carbon atom forms four strong covalent bonds with its neighboring carbon atoms. As a result, diamond has an extremely high melting point (approximately 3,500°C or 6,332°F) due to the strength of the covalent bonds, which require substantial energy to break.
In summary, the melting points of crystals are related to the bonding forces and crystal structure. Crystals with stronger bonding forces, such as metallic or ionic bonds, tend to have higher melting points. On the other hand, crystals held together by weaker bonds, like hydrogen or covalent bonds, have lower melting points. Additionally, the arrangement of atoms in the crystal lattice also affects the melting point.