Question

What bonds are hard to break?

Answer 1

1. The ease of breaking a particular type of bond in a compound is given by the compound's Bond dissociation enthalpy.
2. Bond dissociation enthalpy of a particular type of bond can be defined as the average amount of energy required to break one mole of that type of bond present in the compound.
3. A higher bond dissociation energy means that the bond is harder to break and vice-versa.
4. Among ionic and covalent bonds, ionic bonds tend to be harder to break. This is because ionic bonds form by the complete transfer of electron(s) between the two atoms and as such, there exists an electrostatic force of attraction between the two ions.
5. On the other hand, covalent bonds are made by the sharing of electrons between two atoms. The two atoms are held together by Van der Waals only which are weaker compared to electrostatic attraction.
6. Interestingly there are exceptions to this rule. Take diamond for instance which is a compound made up of carbons bonded covalently to each other in a tetrahedral lattice. Diamond is the hardest material known to us and it does not melt at normal atmospheric pressures due to the strength of the carbon-carbon covalent bonds.
7. On the other hand, a crystal of table salt (Sodium chloride) which is an ionic crystal, will melt at 800 °C. Dissolving it in water is enough to break the ionic bond between Sodium and Chlorine and they form Sodium ions (${\mathrm{Na}}^{+}$) and chloride ions (${\mathrm{Cl}}^{-}$).
8. Thus, it cannot be said definitely that one bond is stronger than the other in a general sense because bond strength depends on more than just the force of attraction that constitutes the bond.
9. Thus, a compound with higher bond dissociation enthalpy will have bonds that are harder to break. Among ionic and covalent bonds, the bond strength varies from compound to compound and it cannot be said definitely that one is stronger than the other.