It depends on the element.
After the IUPAC rules, atomic mass is an expression used only for the mass of isotopes (in atomic mass units).
An atom of carbon-12 has a mass of exactly 12 atomic mass units. This is now the standard.
Atomic mass of an element is calculated based on the mass of it's protons and neutrons. This is why we get isotopes. But I think you are talking about Carbon; the periodic table is based on 12.
The standard atomic weight of darmstadtium is considered 281.
The expression atomic mass is used only for isotopes; the atomic mass is the mass of an atom expressed in unified atomic mass units - (1 amu = 1/12 atomic mass of carbon-12).For elements the expression is atomic weight; the unit is the same.
The number of protons and neutrons in the atom can be determined from the atomic mass. The atomic mass represents the average mass of the isotopes of that element in atomic mass units.
The atomic mass of chlorine is calculated based on the average mass of all the naturally occurring isotopes of chlorine and their relative abundance in nature. Isotopes are atoms of the same element with different numbers of neutrons in their nucleus, which affects their atomic mass. The average atomic mass of chlorine is approximately 35.45 atomic mass units.
isotopes always have the same? mass # & atomic #, or atomic # and atomic weight, or atomic # but different mass #'s
The atomic mass of the most common form of hydrogen is 1. There are isotopes of hydrogen with a mass of 2 (deuterium) and 3 (tritium), but they are rare.
The atomic mass of an isotope is the weighted average mass of all the isotopes of that element based on their natural abundance. It is expressed in atomic mass units (amu).
The atomic mass of an element is the average mass of an element's isotopes, weighted by their natural abundance. It is expressed in atomic mass units (u) and is often close to the mass number of the most abundant isotope of the element.
When atomic mass is expressed in unified atomic mass units, it is similar to isotopic mass and has the same numerical value as that of atomic mass. The atomic mass or the relative isotopic mass is the mass of one atom which at a time can be only one isotope.