Atomic Foundations of Matter | Class 9 Science Notes

Properties of the Ionic and the Covalent Compounds

Ionic and covalent compounds exhibit distinct physical properties due to differences in bonding. Ionic compounds like sodium chloride and copper sulfate are generally soluble in water but insoluble in non-polar solvents like kerosene and petrol. They do not conduct electricity in solid state because ions are fixed in the crystal lattice but conduct electricity when dissolved in water or molten due to free ions. Covalent compounds such as camphor and naphthalene are usually insoluble in water but soluble in non-polar solvents and do not conduct electricity in solid or solution form because they do not produce ions. Ionic compounds have high melting and boiling points due to strong electrostatic forces, whereas covalent compounds have lower melting and boiling points. These properties are demonstrated through experiments testing solubility and electrical conductivity. Understanding these differences helps in identifying the nature of compounds and their applications.

📊 Diagram: Table on page 17 (9×6) showing solubility and electrical conductivity of compounds; Fig. 9.16: Ionic compounds sodium chloride and copper sulfate; Fig. 9.17: Covalent compounds camphor and naphthalene

🧪 Activity: Activity 9.4: Test solubility of various compounds in water, kerosene, and petrol, and test electrical conductivity in solid state and in aqueous solution.

🔗 Connection: This section leads to the concepts of molecular mass and formula unit mass.

Table on page 17 (9×6)