No, elemental atoms typically do not have whole number masses or mass numbers. The mass of an atom is determined by the combined masses of its protons, neutrons, and electrons. Since protons and neutrons have masses that are close to 1 atomic mass unit (amu), and electrons have a much smaller mass, the total mass of an atom is usually not a whole number.
The mass number of an atom, denoted by the symbol A, represents the total number of protons and neutrons in the nucleus of the atom. It is a whole number. However, the atomic mass of an element, which is the average mass of all the isotopes of that element, is often not a whole number due to the existence of different isotopes with different masses and abundances.
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. Since the atomic mass of an element is a weighted average of the masses of its isotopes, the resulting atomic mass is often a decimal or fractional value. The decimal values arise from the fact that different isotopes have different abundances in nature, and their contributions to the average mass are taken into account.
For example, the atomic mass of carbon, which has two common isotopes (carbon-12 and carbon-13), is approximately 12.01 atomic mass units. This value reflects the weighted average of the masses of the carbon-12 and carbon-13 isotopes, considering their relative abundances.
So, while individual atoms of an element may have whole number masses or mass numbers (corresponding to a specific isotope), the atomic mass and average mass of the element as a whole are typically not whole numbers due to the presence of different isotopes.