Ionic Solids
Ionic solids are crystalline structures formed by the electrostatic attraction between oppositely charged ions. These ions are typically created when a metal loses electrons to become positively charged cations, while a nonmetal gains these electrons to become negatively charged anions. The classical example mentioned, limestone ((CaCO_3), consists of calcium ions ((Ca^{2+}) and carbonate ions ((CO_3^{2-}). This arrangement results in a solid with a high melting point due to the strong ionic bonds and is typically poor in electrical conductivity when solid but can conduct when molten or in solution.
Network Solids
Network solids, also known as covalent network solids, are compounds where atoms are connected by covalent bonds in a continuous network that extends throughout the material. Quartz ((SiO_2) is a prime example, featuring a three-dimensional network of silicon and oxygen atoms. This type of solid is noted for its hardness and high melting points because of the strength of the covalent bonds that hold the network together, making substances like diamonds and quartz very durable.
Molecular Solids
Molecular solids are comprised of molecules held together by intermolecular forces rather than strong ionic or covalent bonds. The molecules within these solids, such as dry ice ((CO_2) or sucrose ((C_{12}H_{22}O_{11}), are discrete and have relatively low melting and boiling points. These solids are generally soft and often volatile. The intermolecular forces at work include London dispersion forces, dipole-dipole interactions, and hydrogen bonding, which are significantly weaker than the bonds in network or ionic solids.
Polymeric Solids
Polymeric solids are materials made up of long, repeating chains of smaller units known as monomers. Polyethylene, with its repeated (-CH_2CH_2-) units, is a common type of polymeric solid. These chains can be linear, branched, or cross-linked, affecting the polymer's properties. Their mechanical strength and melting point largely depend on the interactions between the polymer chains, which can include covalent bonds and various intermolecular forces.
Crystal Lattice
The crystal lattice is the framework within a solid where atoms, ions, or molecules are arranged in a highly ordered, repeating pattern. This structure extends in all three spatial dimensions and is fundamental to understanding the properties of the solid. For example, the strength of the lattice in ionic solids dictates their rigidity and high melting points, while the more flexible arrangements in molecular solids lead to softer materials.
Covalent Bonds
Covalent bonds are chemical bonds formed by the sharing of electron pairs between atoms. They are the primary bonding type found in network solids and are instrumental in materials like diamond and quartz, providing robust and durable structures. Polymers also utilize covalent bonds within the backbone of their molecular chains, which gives them the ability to form extensive structures capable of bearing load and stress.
Intermolecular Forces
Intermolecular forces are the attractions between molecules, which, unlike ionic or covalent bonds, do not involve the sharing or transfer of electrons. These forces are crucial in molecular solids, such as sucrose and dry ice, where they govern the physical properties like melting and boiling points, solubility, and vapor pressure. Although weaker than chemical bonds, intermolecular forces play a significant role in the phase transitions and the state of matter of these solids.
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