In general, the atomic mass of an element is approximately equal to the sum of the number of protons and neutrons in its nucleus, while the atomic number corresponds to the number of protons. It is uncommon, but there are a few cases where an element may have an atomic mass greater than its atomic number. Here are a few examples:
Technetium (Tc): Technetium is a synthetic element with atomic number 43. Its most stable isotope, technetium-98, has an atomic mass of 97.9072 atomic mass units (amu), which is slightly less than the atomic number. Technetium is one of the few elements that does not have any stable isotopes.
Promethium (Pm): Promethium is another synthetic element, and it has an atomic number of 61. The most stable isotope of promethium is promethium-145, which has an atomic mass of 144.91276 amu, again slightly less than the atomic number. Promethium is also a rare element and does not occur naturally.
These are the only two elements in the periodic table that have atomic masses slightly less than their atomic numbers. Other elements generally have atomic masses greater than their atomic numbers due to the presence of additional neutrons in their nuclei, but the difference is typically more significant than a slight discrepancy.
Please note that the information provided is accurate , and any recent discoveries or findings may not be included.