Ions and Ionic Bonds

Ions and Ionic Bonds


  • An ion is an atom or group of atoms that have either lost or gained electrons, giving it a net charge.
  • When an atom loses one or more electrons, it becomes a positive ion or a cation.
  • When an atom gains one or more electrons, it becomes a negative ion or an anion.
  • The number of protons remains the same during ion formation, it’s the electron count that changes.
  • Isotopes can also form ions by gaining or losing electrons.
  • Transition metals, found in Groups 3-12 of the Periodic Table, can form multiple types of ions with different charges.

Ionic Bonds

  • An ionic bond is the electrostatic force of attraction between oppositely charged ions. It typically occurs between a metal and a non-metal.
  • The formation of an ionic bond involves the donating and accepting of electrons. The metal atom donates, and the non-metal atom accepts to complete their outer electron shells.
  • The structure formed by the ions in an ionic compound is called an ionic lattice. This lattice is a regular repeating pattern of ions, extending in three dimensions.
  • Ionic compounds tend to have high melting and boiling points because of the strong electrostatic forces holding the ions together in the lattice.
  • Most ionic compounds are soluble in water because water molecules can pull the ions away from the lattice.
  • An ionic compound in the molten state or dissolved in water can conduct electricity because the ions are free to move and carry charge.

Writing Ionic Formulas

  • When writing the formula for an ionic compound, the overall charge should be zero, as compounds are neutral.
  • The charge of each ion is considered to ensure the compound is neutral. If one ion is +2 and the other is -1, for example, it would require two of the -1 charged ions to balance the charge.
  • In a stable ionic compound, the sum of the charges on the cations is equal to the sum of the charges on the anions.
  • The formula of an ionic compound is written as the symbol of the cation followed by the symbol of the anion.
  • Subscripts are used to indicate the number of ions needed to balance the charge in the compound.
  • For example, the formula for sodium chloride is NaCl because one sodium ion (Na+) and one chloride ion (Cl-) are needed to balance the charge.