Ionic Compounds: Properties and Concepts

Key Properties of Ionic Compounds

1. Melting and Boiling Points

• High melting and boiling points due to strong forces of attraction between oppositely charged ions.
• Stronger attraction results in higher melting and boiling points for ionic compounds.

2. Electrical Conductivity

• Electrical conductivity is negligible in solid state.
• Ionic compounds conduct electricity in molten state and when dissolved in water (aqueous solution).
• No conductivity in solid state due to strong ionic bonds preventing charge movement.
• Conductivity requires mobility of charges (ions/electrons) which is not possible in solid state.
• Impurities may allow for limited conductivity in solid state.

3. Solubility

• Ionic compounds are soluble in polar solvents (e.g., water).
• Not soluble in non-polar solvents due to lack of charge separation.
• "Like dissolves like": Polar ionic compounds will dissolve in polar solvents.
  • Water is a common example of a polar solvent (high dielectric constant).

4. Hydration Process

• Hydration: The process of solvent (often water) surrounding and interacting with ions to separate them.
• Dielectric Constant: The ability of a solvent to separate charges.
  • Water has a high dielectric constant (82), making it an excellent solvent for ionic compounds.
• Energy is released during hydration, known as hydration enthalpy.
• The solubility of ionic compounds depends on both hydration enthalpy and lattice enthalpy.

5. Reactions of Ionic Compounds

• Ionic reactions involve ions, making them typically fast.
• Example: Mixing NaCl and AgNO3 in aqueous solution results in immediate formation of AgCl precipitate.

6. Isomerism

• Ionic compounds do not exhibit isomerism due to the non-directional nature of ionic bonds.
• Covalent bonds, in contrast, are directional and can exhibit isomerism.

7. Variable Electrovalency

• Variable Electrovalency: Some metals can exhibit different valencies in their compounds (e.g., Fe, Cu, Sn).
• Factors influencing variable valency include electronic configuration and inert pair effect.
  • Example: Fe can show +2 and +3 oxidation states.
• Inert pair effect: Heavier elements exhibit decreased reactivity due to poor shielding from d and f electrons.

Covalent Bonding

1. Covalent Bond Formation

• Covalent bonds are formed by the equal sharing of electrons between non-metals.
• Overlapping of atomic orbitals leads to bond formation.
• Types of bonds:
  • Single bond: Sharing of one pair of electrons.
  • Double bond: Sharing of two pairs of electrons.
  • Triple bond: Sharing of three pairs of electrons.

2. Lewis Structures

• Steps to Draw Lewis Structures:
  1. Calculate total number of valence electrons.
  2. Determine the central atom (less electronegative or with higher valency).
  3. Distribute electrons to achieve complete octets (or duplets for H).
  4. Form multiple bonds if necessary to complete octets.
• Examples of Lewis structures can include CO2 and SO42-.

Conclusion

• Understand the properties, reactions, and bonding of ionic compounds.
• Learn to differentiate between ionic and covalent compounds, especially in terms of structure and bonding behavior.