COMPOUNDS

5.1 - Ionic Bonding

Some general points can be made about ionic compounds:

• The smallest unit of an ionic compound is a formula unit. The mass of this formula unit is called the formula mass.
  ( We will discuss more about formula mass in section 7.1.)
  
  • The formula unit of sodium chloride is NaCl. It has a formula mass is 58.44 amu/formula unit.
  • The formula unit of sodium chloride is MgCl₂. It has a formula mass is 95.21 amu/formula unit.
    
    
• The strong attractions between the cations and the anions in ionic solids are responsible for their high melting points. For ionic compounds, melting points typically range from 300^oC to 1000^oC.
• Ionic compounds are soluble in water.
• In aqueous solution, an ionic compound dissociates into its ions.
  
  • This means that when NaCl is dissolved in water, the solution contains Na⁺ ions and Cl^- ions.
    
    
• The dissociated ions in aqueous solution gives the solution the ability to conduct electricity. Therefore, ionic compounds dissolved in water makes strong electrolytes.

Section 6.4
The Ionic Bond ..p124

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