ACS Chemistry Practice Exam 2026 – The All-in-One Guide to Exam Success!

The formation of an ionic bond is most likely when an element with low ionization energy interacts with an element that has high electron affinity. An element with low ionization energy readily loses electrons to form positive ions (cations) because it requires little energy to remove an electron. In contrast, an element with high electron affinity has a strong tendency to gain electrons, thus forming negative ions (anions).

When these two types of elements come into contact, the cation formed from the element with low ionization energy will attract the anion formed from the element with high electron affinity. This electrostatic attraction between oppositely charged ions is what characterizes an ionic bond. The result is the formation of a stable ionic compound.

In contrast, covalent bonds involve the sharing of electrons between two nonmetals, metallic bonds involve the pooling of electrons among a lattice of metal atoms, and hydrogen bonds are a type of weak intermolecular force typically occurring between molecules containing hydrogen bonded to highly electronegative atoms. None of these would typically form in a scenario involving one element that is likely to lose an electron and another that is likely to gain one.