In most cases, atomic masses are not whole numbers. Atomic masses represent the average mass of all the isotopes of an element, taking into account their relative abundances. Isotopes are atoms of the same element that have different numbers of neutrons.
For example, the atomic mass of chlorine is approximately 35.45 amu. This value is a weighted average of the masses of the two naturally occurring isotopes of chlorine: chlorine-35 and chlorine-37.
While it is common to round atomic masses to the nearest whole number for simplicity, it is important to recognize that the precise atomic mass may contain decimal values. In academic or scientific contexts, it is generally recommended to use the more accurate decimal values for atomic masses.
In summary, while you may encounter atomic masses rounded to whole numbers for convenience or simplicity, it is essential to be aware of the actual decimal values associated with atomic masses for accurate scientific understanding.