Polarisation

• Polarisation refers to the distortion of the electron cloud around an atom or ion by another nearby atom or ion.
• The entity causing the distortion is known as the polarising ion, while the ion being distorted is the polarised ion.
• Factors affecting polarisation include: charge density of the polarising ion, size of the polarised ion, and the shape of the ions’ orbitals.
• The higher the charge and smaller the size of the polarising ion, the greater the polarising power. Conversely, the larger the size of the polarised ion, the greater its polarisability.
• Polarisation plays a significant role in determining the type of bonding in a compound.
• If polarisation is significant, the compound typically has some covalent character – even if it may be classified as an ionic compound.
• This covalent character in ionic compounds can be explained using Fajans’ rules.
• According to these rules, if the polarising ion is small and highly charged, and the polarised ion is large and of low charge, there is a greater probability of covalent bonding.
• The concept of polarisation is pivotal when studying lattice energies and predicting the solubilities of salts.
• The degree of polarisation can also affect the physical properties of ionic compounds, including melting points and solubility in water.

Remember to engage with this matter interactively to ensure understanding: practise drawing ion models considering the factors affecting polarisation, review the Fajans’ rules regularly, and solve problems related to predicting bonding types and solubilities of salts.