ACS Chemistry Practice Exam 2025 – The All-in-One Guide to Exam Success!

A chemical bond forms between two atoms primarily when their electron probabilities overlap. This overlap allows for the sharing or transfer of electrons, which is the fundamental mechanism behind the formation of covalent and ionic bonds. In a covalent bond, for example, two atoms may share one or more pairs of electrons, leading to stability as both atoms achieve a more energetically favorable electron configuration.

The overlap of electron probabilities plays a crucial role in the lower potential energy of the bonded atoms compared to their energy when they are separate. This interaction essentially creates a strong attractive force that holds the two atoms together, thereby forming a stable chemical bond.

In contrast, the other options do not accurately describe the conditions necessary for bond formation. When atoms are at a large distance from each other, they tend to exist as separate entities with no significant interaction. The equality of atomic masses does not impact the bond formation directly, as bonding is more related to electronic configuration rather than mass. Lastly, the possession of different energy levels alone does not lead to the bonding of atoms; rather, it is the interaction of their electron clouds that plays a critical role.