Unit-2 chapter-4 Pg:- 82.83 half
Ionic substances are formed by the attraction between positively charged ions (cations) and negatively charged ions (anions). These strong electrostatic forces of attraction result in several characteristic properties of ionic compounds.
High Melting and Boiling Points:A lot of energy is required to overcome the strong electrostatic forces between the ions in a solid ionic compound. This translates to high melting and boiling points for ionic substances. For example, table salt (NaCl) has a melting point of 801 °C (1474 °F) and a boiling point of 1465 °C (2669 °F).
Hardness and Brittleness: The strong ionic forces make ionic crystals rigid and hard. However, these crystals can cleave easily in specific directions because the forces between ions are strongest in certain orientations. This makes ionic compounds brittle, meaning they can shatter when struck with force.
Electrical Conductivity: In the solid state, the ions in an ionic compound are fixed in their positions and cannot move freely. Therefore, solid ionic compounds are insulators and do not conduct electricity. However, when ionic compounds are melted (liquid state) or dissolved in water (aqueous solution), the ions become free to move and conduct electricity. The solution or melt is then called an electrolyte.
Solubility in Water: Ionic compounds are generally soluble in water. The polar water molecules can surround the charged ions and weaken the electrostatic forces between them, causing the ionic compound to dissociate into separate ions in solution.
Crystal Structure: Ionic compounds form crystals with a highly ordered structure. The positive and negative ions are arranged in a repeating three-dimensional pattern that minimizes electrostatic repulsion and maximizes electrostatic attraction.