Question

In general, the higher the charge on the ions in an ionic compound, the more favorable the lattice energy. Why do some stable ionic compounds have \(+1\) charged ions even though \(+4,+5\), and \(+6\) charged ions would have a more favorable lattice energy?

Short answer

In summary, although higher charged ions (+4, +5, and +6) provide a more favorable lattice energy, stable ionic compounds may still have +1 charged ions due to the balance between ion formation energy (ionization energy and electron affinity) and lattice energy. Lower ionization energy and electron affinity for certain elements facilitate the formation of +1 charged ions, which may offset the lower lattice energy. Furthermore, factors like ion size and crystal structure also impact the overall stability of an ionic compound.

Step-by-step solution

Understand lattice energy

Lattice energy is the energy required to separate ions in an ionic compound and is an indicator of the stability of the compound. The greater the lattice energy, the more stable the ionic compound. In general, lattice energy increases with the charge of the ions and with the decrease in ionic radius.

Consider the energy involved when higher charged ions form

When ions with a higher charge form an ionic compound, they would have a more favorable lattice energy because the electrostatic attraction between the ions would be greater. However, forming ions with higher charges also requires a significant amount of energy. This energy comes from ionization energy (removing electrons) and electron affinity (adding electrons). Removing or adding electrons to an atom requires energy, and the energy required increases with the charge of the ion.

Balance between energy required to form ions and lattice energy

While an ionic compound with higher charged ions would have a more favorable lattice energy, the overall stability of the compound depends on the balance between the energy required to form the ions and the lattice energy. For some elements, especially those in the lower periods of the periodic table, the ionization energy and electron affinity are relatively low, making it easier to form +1 charged ions despite a lower lattice energy.

Consider additional factors affecting stability

Other factors, such as size of the ions and the crystal structure of the ionic compound, also influence the stability of an ionic compound. +1 charged ions have larger sizes compared to higher-charged ions, leading to weaker electrostatic attractions between the ions and hence, lower lattice energy.

Conclusion

In conclusion, some stable ionic compounds have +1 charged ions even though +4, +5, and +6 charged ions would have a more favorable lattice energy because the overall stability of an ionic compound depends on a balance between the energy required to form the ions and the lattice energy. In some cases, the lower ionization energy and electron affinity of +1 ions offsets the lower lattice energy, making it energetically favorable to form these ions. Moreover, other factors such as size of the ions and the crystal structure of the ionic compound also contribute to the overall stability.