Ionic Compounds

A compound is a substance made up of two or more different elements bonded together. An ionic compound is formed when atoms are connected by ionic bonds, which occur between positively charged ions (cations) and negatively charged ions (anions).

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Properties of Ionic Compounds

Here are some properties of ionic compounds:

  • Form through ionic bonding between two or more atoms.
  • Typically involve metals from Groups 1 and 2 bonding with non-metals from Groups 6 and 7.
  • Possess high melting and boiling points due to the strength of the ionic bonds.
  • Are solid at room temperature.
  • Can conduct electricity when melted or dissolved in water (aqueous solution), because the ions, which are charged particles, are free to move.
An infographic showing the properties of ionic compounds. At the top, a red Na+ ion and a blue Cl- ion are connected by an ionic bond with a metallic clamp trying to break it, with the text 'Ionic bonds are very strong.' To the right, a curved arrow between the Na+ and Cl- ions indicates that ionic compounds are composed of a metal and a non-metal. Below, two beakers illustrate the solubility and conductivity properties of ionic compounds: the left beaker shows that ionic compounds dissolve in water, with clear water in the beaker, and the right beaker shows solid ionic compounds not conducting electricity, represented by an undissolved pile at the bottom, alongside text that says ionic compounds conduct electricity in an aqueous state, represented by the pile beginning to dissolve in water.

Strong Bonds

Ionic bonds are incredibly strong due to the electrostatic attraction between cations and anions. This strength results in high melting and boiling points for ionic compounds. It requires a significant amount of energy to transition an ionic compound from solid to liquid and from liquid to gas.

Ionic compounds typically organise into lattice structures, held together by these bonds in a regular repeating pattern. Disrupting this structure to melt the compound requires breaking many ionic bonds simultaneously. This explains the high energy needed to melt the compound and therefore the high melting point of ionic compounds.

The strength of ionic bonds increases with the charge of the ions involved. For example, sodium chloride (NaCl), with Na⁺ and Cl⁻ ions, melts at 801 °C, while magnesium oxide (MgO), with Mg²⁺ and O²⁻ ions, requires a much higher temperature of 2,852 °C to melt due to its stronger ionic bonds.

Conduction of Electricity

Since ions are charged particles, they can conduct electricity; but for this to happen, they need to be able to move freely.

In solid ionic compounds, ions are fixed in place within the lattice structure and cannot conduct electricity. However, when an ionic compound is in liquid form or dissolved in water (creating an aqueous solution), the ions are free to move, allowing the compound to conduct electricity effectively.

This explains why substances like sodium chloride (table salt) can conduct electricity when dissolved in water or melted but not in their solid form.

An illustration shows the process of salt (NaCl) dissolving in water (H2O). On the left, a beaker of water with a pile of salt at the bottom is depicted. A magnified view on the right side shows the detailed interaction at the molecular level: water molecules, indicated by 'H2O' with red oxygen and small grey hydrogen atoms, surround individual sodium (Na+) and chloride (Cl-) ions, extracting them from the salt's crystalline structure into the solution. The sodium ions are shown in green, chloride ions in pink, and water molecules in red and grey, highlighting the process of salt dissolving in water.

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