Which bond is stronger? [closed]

Question

Are ionic bonds stronger than covalent bonds?

I googled it and found various answers, some saying it is stronger and some saying it’s not.

Answer 1

Generalisations are impossible. There are many examples of strong and weak bonds in both ionic and covalent compounds

There are a number of problems with the question. One is that there bonding is not an either/or concept: there is a something of a continuum between "pure" ionic and "pure" covalent bonding. There is also a lot of confusion about what sort of bonds make a solid. Many "covalent" solids are made of molecules with covalent bonds but the solid exists because of weaker forces between the individual molecules.

Even if we ignore molecular solids the bulk properties are determined by the weak bonds between molecules, there are a wide variety of different behaviours. It is often assumed that ionic bonding is "stronger" because many familiar ionic compounds (like sodium chloride) are high melting-point solids. But many compounds with networks of covalent bonding are also refractory solids, like diamond. Some even show both weak and strong bonds in the same compound (graphite has weak bonds between the planes of carbon hexagons but the hexagonal planes are very strongly bonded). So, both ionic and covalent examples exhibit very strong bonds.

But the opposite is also true. Ionic compounds with large, floppy ions are often liquids suggesting that "weak" bonds are possible in ionic compounds. Examples like 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) are liquids at room temperature.

Also some covalent compounds have such weak bonds that they can only be observed at very low temperatures. Some argon covalently bonded compounds have only been observed in frozen argon.

The point being that you can't generalise. Some ionic compounds have strong bonds and others have weak bonds. Some covalent bonds are very strong, some are very weak.

Answer 2

Part of the reason for many answers is that "stronger" can be different things. If we consider a typical two-electron bond between two atoms A and B, it can break in three ways:

1) 1 electron can stay with A and one with B: $\ce{A-B -> A. + B.}$

This is called homolytic bond cleavage.

2) Both electrons can stay with A: $\ce{A-B -> A- + B+}$

This is called heterolytic bond cleavage.

3) Both electrons can stay with B: $\ce{A-B -> A+ + B-}$

This is another example of heterolytic bond cleavage.

If you look at tables of "bond strength", they usually report the enthalpy change for the homolytic cleavage reaction indicated above.

That value is typically larger for ionic bonds than covalent bonds, because ionic bonds form when both electrons have more density on the same atom in the bond. In order to break the bond homolytically, one electron has to go up substantially in energy to stay with the more positive atom.

In contrast, in a covalent bond, the electrons are shared nearly equally between the atoms, so, while bond breaking still takes a lot of energy, it is easier to end with one electron on each atom.

If, on the other hand, we look at the heterolytic cleavage, ionic bonds are much easier to break, since they already have both electrons mostly on one atom. The major energetic cost of breaking the bond is just the energy required to separate the charges from one another. For the covalent bond, we have the same cost of charge separation, but additionally we need to force both electrons onto one atom.

Answer 3

Usually ionic bonds are stronger than covalent bonds. But there are exceptions. Quartz SiO2 for example is made of covalent bonds, and it melts at very high temperature (> 1400°C). I am afraid there are no general rules.

Answer 4

Covalent bond is defined as the sharing of electrons between two atoms (non metals). Ionic bond is defined as the transfer of electrons from the valence shell of anion(s) to the valence shell of cation(s).

On a covalent bond, there are two types of forces that held the atoms together; (1) intramolecular forces and (2) intermolecular forces. Intermolecular forces are quite weak compare to the intramolecular forces. Also, the atoms on the molecules are not properly held by the intramolecular forces. Covalent bonds can be observed usually on gases, liquids and low melting solids.

On the other hand, anions and cations are held together by electrostatic forces that are usually strong. Ionic bonds can be observed on the solids at room temperature which have high melting points.

Ionic bond is stronger than covalent bond, however, other compounds demonstrate different properties of the bond due to various factors, such as environmental conditions, electronegativity, bond energy, orbitals, etc.