Ionic Bonding  Electrons are transferred  Electronegativity differences are generally greater than 1.7  The formation of ionic bonds is always exothermic!

Determination of Ionic Character Compounds are ionic if they conduct electricity in their molten state Electronegativity difference is not the final determination of ionic character

Coulomb’s Law “The energy of interaction between a pair of ions is proportional to the product of their charges, divided by the distance between their centers”

Table of Ion Sizes

Estimate  H f for Sodium Chloride Na(s) + ½ Cl 2 (g)  NaCl(s) Na(s)  Na(g) kJ Na(g)  Na + (g) + e kJ ½ Cl 2 (g)  Cl(g) + ½(239 kJ) Cl(g) + e -  Cl - (g) kJ Na + (g) + Cl - (g)  NaCl(s) -786 kJ Na(s) + ½ Cl 2 (g)  NaCl(s) -412 kJ/mol

Estimate  H f for Magnesium Fluoride Mg (s) + F 2(g)  MgF 2(s) Mg(s)  Mg(g) kJ Mg(g)  Mg 2+ (g) + 2e kJ F 2 (g)  2F(g) +154kJ 2F(g) + 2e -  2F - (g) 2(- 328)kJ Mg 2+ (g) + 2F - (g)  MgF 2(s ) -3916kJ Mg(s) + F 2 (g)  MgF 2 (s) kJ/mol

Sodium Chloride Crystal Lattice Ionic compounds form solid crystals at ordinary temperatures. Ionic compounds organize in a characteristic crystal lattice of alternating positive and negative ions. All salts are ionic compounds and form crystals.

Properties of Ionic Compounds