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How to Classify Compounds Ionic or Covalent

Chemists define the bonds between atoms using two main categories; covalent or ionic. In covalent bonding, two atoms contribute and equally share a pair of electrons to form the bond between them. In ionic bonding, one atom has a much greater affinity for electrons and so takes an electron from a neighboring atom and becomes negatively charged, while the neighbor becomes positive. The two oppositely charged species are then bonded together by the mutual attraction of their charges. In reality, all bonds are actually located somewhere along a sliding scale between fully covalent and fully ionic. You can determine where a given bond lies by looking at the relative electron affinities of the atoms.

Things You'll Need

Table of elements electronegativity values
Calculator

Instructions

- 1
  Look up values of electronegativity for the two elements which have the adjacent atoms sharing the bond in your compound. Electronegativity is a measure of how strongly an element's atoms attract electrons, and you can get values for this property from charts given in standard chemistry textbooks and reference books. For example, for the chemical sodium chloride (NaCl), you would look up the electronegativity values for sodium (Na is 0.9) and chlorine (Cl is 3.0).
- 2
  Calculate the difference between the two electronegativity values you just looked up. In the case of NaCl, 3.0 - 0.9 = 2.1.
- 3
  Look up the percent ionic character which corresponds to the difference in electronegativities which you just calculated. Tables of elemental electronegativity values such as you used to find the initial electronegativities will also include a chart giving the ionic character of each possible difference in electronegativity. In the case of the NaCl example, you would look up 2.1 and find a related percent ionic character of 67.
- 4
  Compare the percent ionic character for your compound to a benchmark level of 50 percent. If your compound has a percent ionic character greater than this, it can be considered as an ionic compound; otherwise it is considered covalent. NaCl would be considered an ionic compound, since its percent ionic character of 67 exceeds the benchmark of 50.

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