Ionic compounds cannot conduct electricity in their solid state, primarily due to the immobility of ions in the lattice structure. In an ionic solid, ions are held tightly in place by the strong electrostatic forces of attraction, forming a rigid lattice. This fixed positioning means that ions cannot move freely, which is a prerequisite for electrical conductivity. Electrical conductivity in a substance occurs when charged particles are free to move and carry an electric current. In the solid state, the lack of free-moving charged particles prevents the flow of electricity. However, when ionic compounds are melted or dissolved in water, the ions become free to move. This mobility allows them to carry an electric current, enabling ionic solutions or melts to conduct electricity.

The charge of ions in an ionic compound significantly influences its properties. Higher charged ions (like Mg²⁺ and O²⁻ in magnesium oxide) create stronger electrostatic attractions within the lattice, leading to more robust and stable compounds. This increased attraction results in higher melting and boiling points, as more energy is required to overcome these stronger forces. Moreover, compounds with higher charged ions are typically harder and more brittle due to the increased strength of the ionic bonds. In contrast, compounds with lower charged ions (such as Na⁺ and Cl⁻ in sodium chloride) have comparatively weaker ionic bonds, resulting in lower melting and boiling points. The strength of the ionic bond also influences the solubility of the compound in water; generally, compounds with lower charged ions tend to be more soluble. Thus, the charge on the ions is a key factor in determining the physical and chemical properties of an ionic compound.

Ionic compounds dissolve in water due to the polar nature of water molecules, which can interact effectively with the charged ions. Water molecules have a partial negative charge near the oxygen atom and a partial positive charge near the hydrogen atoms. This polarity allows water molecules to surround and interact with the ions in an ionic compound, stabilising them in solution. The positive end of water molecules attracts anions, while the negative end attracts cations. This interaction weakens the electrostatic forces holding the ionic lattice together, leading to the dissolution of the compound. In contrast, non-polar solvents, lacking this polarity, cannot effectively weaken the ionic bonds or stabilise the ions in solution. Therefore, ionic compounds are generally insoluble in non-polar solvents, as these solvents cannot provide the necessary interaction to disrupt the ionic lattice and solvate the ions.

The size of ions significantly impacts the strength of ionic bonding. In general, smaller ions form stronger ionic bonds due to the shorter distance between their nuclei and the outer electrons. This proximity enhances the electrostatic attraction between the positively charged nucleus of one ion and the negatively charged electrons of the other. For example, smaller cations, like Li⁺, can get closer to anions, resulting in a stronger attraction compared to larger cations like Cs⁺. Conversely, larger ions have more electron shells, which can shield the positive charge of the nucleus from the negative charge of the electrons in the anion, thereby weakening the bond. Additionally, in larger ions, the increased distance between the nucleus and the bonding electrons reduces the overall electrostatic attraction, further weakening the bond. Therefore, the size and electron configuration of the ions play a crucial role in determining the strength and characteristics of ionic bonds.

Ionic bonds play a vital role in various biological systems and processes. Many essential biological molecules and structures are stabilised by ionic interactions. For example, ionic bonds are crucial in the formation of cell membranes and in the functioning of ion channels, which regulate the passage of ions into and out of cells. These bonds are also fundamental in muscle contractions, where the movement of calcium ions, in particular, is key. Furthermore, ionic bonds are involved in the stabilisation of the secondary and tertiary structures of proteins and enzymes, which are essential for a wide range of biological activities. Enzyme activity, for instance, often depends on ionic interactions between the enzyme and its substrate or cofactors. Additionally, the transmission of nerve impulses relies on the movement of sodium and potassium ions across nerve cell membranes, a process governed by ionic gradients. Thus, ionic bonds are essential for maintaining the structure and function of living organisms at a molecular level.