Electrostatic force of attraction

The electrostatic force of attraction is the attractive force between particles of opposite charge. In an ionic compound it holds the cations and anions together. Malay: daya tarikan elektrostatik · Chinese: 静电吸引力.

Opposite charges attract, and this simple rule is what an ionic bond is built on. After electron transfer produces positive cations and negative anions, the opposite charges pull towards one another, and that pull is the electrostatic force of attraction. The force is strong because the charges are full charges sitting close together, and it acts throughout the whole giant ionic lattice, not just between one pair of ions. The larger the charges and the smaller the ions, the stronger this force becomes.

Example. In sodium chloride the electrostatic force of attraction acts between every Na⁺ and its neighbouring Cl⁻ ions in all directions. In magnesium oxide the force is even stronger, because Mg²⁺ and O²⁻ carry double charges, which is why magnesium oxide has a much higher melting point than sodium chloride.

Confusion to avoid. When you define an ionic bond you must include the full phrase “strong electrostatic force of attraction between oppositely charged ions”. Writing only that the ions “attract” or “join” loses the mark. Do not confuse this force with the weak intermolecular forces between covalent molecules, which are of a completely different, much smaller size.

Because the force acts equally in every direction and throughout the lattice, a very large amount of energy is needed to overcome it, which is the underlying reason ionic compounds are hard, brittle and high-melting.

The electrostatic force of attraction is the actual bond in every ionic structure of this chapter, and stating it in the exact marking-scheme wording is one of the surest ways to secure a definition mark in SPM Chemistry.