Compounds With Both Ionic and Covalent Bonds

Some chemical compounds contain both ionic and covalent bonds. These are ionic compounds that contain polyatomic ions. Often, a compound with both types of bonds contains a metal bonded to an anion of covalently bonded nonmetals. Less often, the cation is polyatomic. The cation isn’t always a metal. Sometimes nonmetals bond to form a cation with enough electronegativity difference from the anion to form an ionic bond!

10 Examples of Compounds With Ionic and Covalent Bonds

Here are examples of compounds with both ionic and covalent bonds. Remember, an ionic bond occurs when one atom essentially donates a valence electron to another atom. A covalent bond involves atoms sharing electrons. In pure covalent bonds, this sharing is equal. In polar covalent bonds, the electron spends more time with one atom than the other.

• KCN – potassium cyanide
• NH₄Cl – ammonium chloride
• NaNO₃ – sodium nitrate
• (NH₄)S – ammonium sulfide
• Ba(CN)₂ – barium cyanide
• CaCO₃ – calcium carbonate
• KNO₂ – potassium nitrite
• K₂SO₄ – potassium sulfate
• NaOH – sodium hydroxide
• CsI₃ – cesium iodide

For example, in potassium cyanide (KCN), the carbon (C) and nitrogen (N) are both nonmetals, so they share a covalent bond. The potassium atom (K) is a metal, so it bonds to the nonmetallic anion via an ionic bond. X-ray diffraction of KCN crystals verifies this arrangement. The potassium ions are separate from the bonded carbon and nitrogen ions that form the cyanide anion. Compounds with both ionic and covalent bonds form ionic crystals. When these compounds melt or dissolve into water, the ionic bonds break, but the covalent bonds remain intact. In a melted compound, the cation and anion remain attracted to one another, but not enough to organize into a crystal.

Predicting the Type of Chemical Bond

Usually, all you have to do to predict the type of chemical bond between two atoms is compare their electronegativity values.

• Nonpolar covalent bond – If the atoms are identical, there is no electronegativity difference and the bond is covalent. However, the bond is considered nonpolar as long as the electronegativity difference is less than 0.4
• Polar covalent bond – The electronegativity difference is between 0.4 and 1.7. This is the type of bond formed between most nonmetals.
• Ionic bond – The electronegativity difference is greater than 1.7.

You can use a table to see electronegativity values of atoms. The table is great for identifying the type of bond within the cation and the anion when polyatomic ions occur.

But, how can you tell whether a compound contains both ionic and covalent bonds, just by looking at its chemical formula? First, you need to know which elements are metals and which are nonmetals. This is pretty easy, since the only nonmetals are clustered on the right side of the periodic table (the nonmetal, halogen, and noble gas groups). A dead giveaway the compound contains both bonds is when it has a metal cation bonded to an anion that only contains nonmetals. Also, any compound that contains the ammonium (NH4⁺) cation has both ionic and covalent bonds. The nitrogen and hydrogen atoms are joined by covalent bonds. The polyatomic cation is highly electropositive, so it forms ionic bonds with any anion.

References

• Atkins, Peter; Loretta Jones (1997). Chemistry: Molecules, Matter and Change. New York: W.H. Freeman & Co. ISBN 978-0-7167-3107-8.
• Laidler, K. J. (1993). The World of Physical Chemistry. Oxford University Press. ISBN 978-0-19-855919-1.
• Langmuir, Irving (1919). “The Arrangement of Electrons in Atoms and Molecules”. Journal of the American Chemical Society. 41 (6): 868–934. doi:10.1021/ja02227a002
• Lewis, Gilbert N. (1916). “The Atom and the Molecule”. Journal of the American Chemical Society. 38 (4): 772. doi:10.1021/ja02261a002
• Pauling, Linus (1960). The Nature of the Chemical Bond and the Structure of Molecules and Crystals: An Introduction to Modern Structural Chemistry. Cornell University Press. ISBN 0-801-40333-2 doi:10.1021/ja01355a027