Ionic Bonding

Compounds

• A compound is a pure substance that contains two or more elements that are chemically bonded to each other
  • Can be molecules or ions

Types of bonds

Ionic

• Electrons are transferred from one atom to another and the resulting ions are held together with electrostatic forces
• Typically made from a metal and non-metal
• Are commonly identified as having an electronegativity difference (\(\Delta\chi\)) of \(>2\)
• The transfer of electrons is physical as the electrons move from the HOMO of one atom to the LUMO of another

Covalent

• The atoms do not take electrons, but instead the electrons sit between the atoms and are shared

Metallic

• The electrons delocalise and move freely between the interspersed metal atoms

Ionic Compounds

• Compounds made from metal and non-metal elements are typically ionic

• The groups that they’re in can tell the resulting formula, e.g. \(\ce{CaBr2}\) Calcium is in 2A and needs to get rid of two electrons. Bromine is in group 7A and needs to gain two electrons

• Polyatomic ions in a compound makes it an ionic compound, e.g. \(\ce{Ba(NO3)2}\)

  • The nitrate component is a the nitrate ion \(\ce{NO3−}\)
  • The \(\Delta\chi>2\) rule is not quite accurate, as bonding character is not a cutoff, but instead can vary from strongly covalent to strongly ionic