The smallest difference between two elements' atomic masses depends on the specific elements being compared. The atomic masses of elements can vary significantly, so the smallest difference will occur when comparing elements with atomic masses that are closest to each other.
To determine the smallest difference, we can refer to the periodic table and look for adjacent elements. Let's consider the elements closest in atomic mass to illustrate this:
The two adjacent elements with the smallest difference in atomic mass are hydrogen (H) and helium (He). Hydrogen has an atomic mass of approximately 1.008 atomic mass units (u), while helium has an atomic mass of approximately 4.0026 u. The difference between their atomic masses is approximately 4.0026 - 1.008 = 2.9946 u.
Therefore, the smallest difference in atomic masses between two elements is approximately 2.9946 u, which occurs between hydrogen and helium.