Ionic compounds are an important part of chemistry and daily life. From the table salt you sprinkle on your food to the calcium in your bones, ionic compounds play a vital role. These are a fundamental class of chemical compounds which are formed through the electrostatic attraction between oppositely charged ions, typically between metals and nonmetals.
Ionic compounds are chemical compounds made up of ions held together by strong electrostatic forces called ionic bonds. Typically, these bonds form between metals and non-metals, where one atom donates electrons and another accepts electrons. For example, in sodium chloride (NaCl), sodium donates one electron to chlorine, creating a strong ionic bond that forms the familiar table salt.
Before diving into the properties of ionic compounds, it’s important to understand the ionic bonding properties.
This structure and bonding mechanism directly influence the characteristics of ionic compounds that we observe.
The properties of ionic compounds come from the nature of the ionic bonds and the arrangement of ions. Here are some major characteristics:
Let's now explore each of these ionic bonding properties in greater detail.
One of the most notable properties of ionic compounds is their high melting point. The ions in an ionic compound are held together by strong electrostatic forces. To melt an ionic solid, a significant amount of energy is required to overcome these forces. Some of the examples of high melting point ionic compounds are:
The electrical conductivity of ionic compounds varies depending on their state:
Some examples of ionic compounds with electrical conductivity are:
When NaCl is dissolved in water, it dissociates into Na⁺ and Cl⁻ ions, allowing the solution to conduct electricity.
Another important characteristic of ionic compounds is their hardness. Ionic compounds form rigid and strong structures, making them hard. However, they are also brittle. When enough force is applied, layers of ions shift and similar charges align, leading to repulsion and the crystal shattering.
Example:
Sodium chloride (NaCl) crystals can easily crack when struck with a hammer.
Ionic compounds are usually soluble in water because water is a polar solvent. The partial positive charge of hydrogen and the partial negative charge of oxygen in water molecules interact with the charged ions, pulling them away from the crystal lattice.
Potassium chloride (KCl) readily dissolves in water, separating into K⁺ and Cl⁻ ions.
Ionic compounds often form beautiful, well-organised crystals. The three-dimensional arrangement ensures that each positive ion is surrounded by negative ions and vice versa, optimising stability.
Unlike covalent compounds that might vaporise easily, like perfumes or alcohols, ionic compounds are typically non-volatile. Their strong ionic bonds prevent them from evaporating at room temperature.
Sodium chloride (NaCl) remains solid and stable at room temperature, showing negligible vapour pressure.
Most ionic compounds tend to have higher densities than molecular compounds. This is because ions are tightly packed in a crystal lattice, maximising space usage.
Barium sulfate (BaSO₄) has a density of 4.5 g/cm³, which is quite high compared to many organic compounds.
The properties of ionic compounds make them useful across various industries:
(Session 2025 - 26)