Ionic Bonds

Chemical Bonds  The force that holds two atoms together is called a chemical bond.

Ionic Bond  The electrostatic force that holds oppositely charged particles together in an ionic compound is called an ionic bond.  Most ionic compounds are called salts.

Properties of Ionic Compounds  During the formation of an ionic compound, the positive and negative ions are packed into a regular repeating pattern that balances the forces of attraction and repulsion between the ions. This particle packing forms an ionic crystal lattice, a three-dimensional geometric arrangement of particles.

 Ionic crystals have high melting points and boiling points because the ionic bonds are strong.  When dissolved in water, ionic compounds are electrical conductors because the ions are free to move. An ionic compound whose aqueous solution conducts electric current is called an electrolyte.

 During any chemical reaction, energy is either absorbed or released.  Endothermic or exothermic  Energy changes also occur during the formation of ionic bonds from the ions formed during a chemical reaction.  The energy required to separate one mole of the ions of an ionic compound is referred to as the lattice energy.

Formulas for Ionic Compounds  The simplest ratio of the ions represented in an ionic compound is called a formula unit.  A formula unit for magnesium chloride is MgCl 2.  Because the total number of electrons gained by the nonmetallic atoms must equal the total number of electrons lost by the metallic atoms, the overall charge of a formula unit is zero.

 A monatomic ion is a one-atom ion, such as Mg 2+ or Br -.  The charge is determined by the location of the element on the periodic table.  The transition metals can form several different positive ions.

 Polyatomic ions are ions made up of more than one atom.  The charge given to a polyatomic ion applies to the entire group of atoms.

Naming Ionic Compounds  1. Name the cation first and anion second.  2. Monatomic cations use the element name.  Monatomic anions use the element name plus the suffix –ide.  Transition metals and metals on the right side of the periodic table often have more than one charge; therefore, roman numerals are used to identify the charge.  Use the polyatomic ion name.