No, the atomic mass and mass number are not the same, although they are related concepts.
The mass number of an atom represents the total number of protons and neutrons in the nucleus of an atom. It is typically denoted by the symbol "A." For example, the mass number of an oxygen atom with 8 protons and 8 neutrons is 16.
On the other hand, atomic mass refers to the average mass of all the isotopes of an element, taking into account their relative abundances. It is typically expressed in atomic mass units (amu). The atomic mass is often a decimal number because it considers the different masses of isotopes and their respective abundance in nature.
To clarify with an example, let's consider the element chlorine. Chlorine has two main isotopes: chlorine-35 and chlorine-37, with mass numbers 35 and 37, respectively. The relative abundance of chlorine-35 is about 75%, while chlorine-37 makes up the remaining 25%. The atomic mass of chlorine is approximately 35.5 amu, which is the weighted average of the masses of its isotopes based on their abundance.
In summary, the mass number refers to the total number of protons and neutrons in an atom's nucleus, while atomic mass represents the average mass of all the isotopes of an element, considering their relative abundances.