Ionic compounds typically have high melting and boiling points compared to covalent compounds due to the nature of the ionic bonds in their lattice structure. In ionic compounds, the lattice is formed by the strong electrostatic attraction between positively charged cations and negatively charged anions. These ionic bonds are significantly stronger than the intermolecular forces present in covalent compounds, such as van der Waals forces, dipole-dipole interactions, or hydrogen bonding. Consequently, a substantial amount of energy is required to overcome these strong ionic bonds to change the state of the compound from solid to liquid (melting) or from liquid to gas (boiling). In contrast, covalent compounds, which are generally held together by weaker intermolecular forces, require less energy to break these forces, resulting in lower melting and boiling points. This fundamental difference in bonding types and the strength of the bonds involved is the primary reason for the higher melting and boiling points observed in ionic compounds.

The hardness of ionic compounds is directly influenced by their giant lattice structure. Hardness in this context refers to the resistance of a material to deformation or scratching. In an ionic lattice, the ions are held in place by strong electrostatic forces of attraction between oppositely charged ions. This rigidity and strength of the lattice contribute to the overall hardness of the compound. The closer and more tightly packed the ions are within the lattice, the harder the compound tends to be. Factors like the size of the ions and the charge on the ions affect how closely they can pack together, impacting the hardness. For example, a lattice with small, highly charged ions can pack more densely, resulting in a harder compound. However, it's important to note that while ionic compounds are hard, they are also brittle. This brittleness arises because when a force is applied, it can cause like-charged ions to align, leading to repulsion and cracks in the lattice. Hence, while the giant lattice structure contributes to the hardness of ionic compounds, it also makes them prone to breaking under stress.

The type of lattice structure in an ionic compound significantly affects its properties, including melting and boiling points, solubility, hardness, and electrical conductivity. Different lattice types, determined by the size and charge of the ions involved, result in variations in these properties. For instance, a face-centred cubic lattice, where ions are closely packed, typically leads to higher melting and boiling points due to the stronger electrostatic forces that need to be overcome. The lattice type also influences the coordination number, which is the number of ions immediately surrounding a given ion. A higher coordination number usually translates to a more stable and robust lattice, impacting the compound's hardness and brittleness. Additionally, the type of lattice affects the solubility of the compound in various solvents. A more tightly bound lattice structure may be less soluble as it is harder for the solvent molecules to disrupt the lattice and solvate the ions. Finally, the lattice structure impacts electrical conductivity. In a solid state, the immobility of ions in a rigid lattice prevents conductivity, while in a molten state or when dissolved, the free movement of ions facilitates electrical conduction. Hence, the specific lattice structure of an ionic compound is a key determinant of its physical and chemical properties.

The giant lattice structure of ionic compounds plays a crucial role in their solubility in water. When an ionic compound is introduced to water, the polar water molecules interact with the ions in the lattice. Water molecules, having a positive and a negative end due to their polar nature, are attracted to the oppositely charged ions in the lattice. This interaction leads to the weakening of the electrostatic forces holding the lattice together. If the attraction between the water molecules and the ions is strong enough to overcome these forces, the ions are pulled away from the lattice and dissolve in water. The degree of solubility depends on the strength of the ionic bonds in the lattice and the ion-dipole forces between the ions and water molecules. Strongly bonded ions in a tight lattice structure, like in some high melting point compounds, may have lower solubility. Conversely, compounds with less tightly bound ions dissolve more readily. The process of dissolving also involves the hydration of ions, where water molecules surround and stabilize the ions in solution.

The size of ions, or ionic radii, significantly influences the structure and properties of an ionic lattice. In a lattice, smaller cations often fit into the spaces between larger anions. This fitting determines the type of lattice that forms and its coordination number, which is the number of ions surrounding a given ion. For instance, in a lattice where small cations are surrounded by larger anions, a high coordination number is observed, leading to a more compact and stable structure. The size difference also affects the melting and boiling points of the ionic compound. A smaller size difference between cations and anions usually results in a closer packing of ions, leading to stronger electrostatic forces. Consequently, more energy is required to overcome these forces, resulting in higher melting and boiling points. Moreover, the size of ions impacts the hardness and brittleness of the compound. Smaller ions can pack more tightly, making the lattice harder but also more brittle, as the ions are less able to shift without breaking the lattice structure.