Which Chemical Bond is Stronger: Ionic vs. Covalent Bonds

The difference between ionic and covalent bonds isn't as complex as you'd think. Image by Decoded Science

The difference between ionic and covalent bonds isn’t as complex as you’d think. Image by Decoded Science

Almost all the atoms found in nature, left alone to themselves, are stable structures. If they always remained such, there would be no need of chemists.

Fortunately, when in close contact, atoms can react in a number of ways.

Often they link to each other in various combinations through bonding, forming molecules called compounds.

Such interaction requires explanation, and so provides employment to humans educated in this field: The field called chemistry.

Chemical Bonds: Ionic and Covalent

There are a variety of ways atoms bond to one another. Some bonds are weaker, and some are stronger. Two of the strongest forms of chemical bond are the ionic and the covalent bonds. Chemical bonds form between two atoms, each with its own electron environment.

  • If each of the two atoms shares an electron with the other atom nearly equally, the bond is called covalent.
  • If one atom exerts considerable force over the other atom’s electron, while the other atom strives to give its electron over, the bond is largely ionic.

Which form of bond—covalent or ionic—is the stronger? The easy way to determine that is to measure the energy it takes to break the bond. That quantity is called bond dissociation energy. The greater the energy it takes to break the bond, the stronger that bond must be. It turns out that most ionic bonds are considerably more difficult to break than covalent bonds.

Ionic Bonds: Electronegativity

In the 1930s, Dr. Linus Pauling expounded on the quality he called electronegativity. Some atoms, if they can be humanized, desire to increase their electron density. Others desire the exact opposite. He developed a list of numbers that quantified that affinity. The presence of appreciable electronegativity favors ionic bond formation.

The simplest way to determine which of the ionic bonds are strongest is to examine the electronegativities of the anion (the negative portion of a compound) and its cation (the positive portion of the compound).

Linus Pauling - Library of Congress

Linus Pauling developed a list of numbers that quantified the property of electronegativity. Image courtesy of the U.S. Library of Congress

Alkali Metals and Halogens

The alkali metals are the least electronegative elements found in the periodic table, whereas the halogens are the most electronegative elements. We list three combinations of these elements, lithium iodide, potassium chloride and rubidium fluoride.

Lithium iodide———-352 kilojoules per mole
Potassium chloride—-427 kilojoules per mole
Rubidium fluoride—–494 kilojoules per mole

Stronger than even these should be the ionic bond in the compound francium fluoride. It is the most electropositive of the elements. Hence, it follows that francium is the least electronegative element, as well.

Chemical Bonds and Electronegativity

In chemistry, we study the interactions between atoms. Elements stick together via chemical bonds; covalent and ionic, including Linus Pauling’s electronegative elements. Which bonds are the strongest? It depends on their properties.

Resources

University of Buenos Aires. Properties of Atoms, Radicals, and Bonds. Accessed October 15, 2013.

Linus Pauling. The Nature of the Chemical BondElectronegativity: Narrative. Oregon State University. Accessed October 15, 2013.

© Copyright 2013 Vincent Summers, All rights Reserved. Written For: Decoded Science

Comments

  1. DS says

    Covalent bonds an ionic bonds are fairly equal in terms of strength, the reason covalent bonds are “weaker” (mp/bp) is actually due to most covalent compounds being simple molecular compounds. This means they are comprised of a maybe a dozen atoms or so…the molecule itself won’t decompose but it will melt due to intermolecular forces being weak, ionic compounds are all bonded together and every ion is bonded to 6 ions around it, meaning they have higher melting points. If you think about it giant covalent structures like diamond and silicon dioxide have very high melting points because even though they are covalent, every atom is bonded to the ones around it. So they aren’t weaker.

  2. john sisith says

    When the strength of ionic bond increases, its ionic nature decreases and covalent nature increases. But why covalent bonds are less stronger?

  3. derek says

    “The greater the energy it takes to break the bond, the stronger that bond must be. It turns out that most ionic bonds are considerably more difficult to break than covalent bonds.”

    That doesn’t really make sense. Covalent bonds are stronger than ionic and covalent bonds should have higher energy.

    • Chris says

      Think of it as if it is a magnet. Ionic bonds are between a metal and a non-metal. Metals generally need to lose electrons while non-metals need to gain them. this makes metals and non-metals attract, kinda like a magnet. The atoms exchange electrons and become ions, the metal has a positive charge because it has more protons than electrons, and the non-metal gains an electron and now the electrons are more numerous than the protons. The atoms then pretty much act like a magnet because one is positive and one is negative, so the stick together because opposites attract.

      covalent bonds are shared electrons between two non-metals, they share the electron(s) to become stable, but both are negatively charged atoms, so the attraction is less. you don’t have the same magnetic styled attraction. I hope this kinda made things a bit clearer.

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