One atomic mass unit is equal to one twelfth of the mass of an atom of carbon 12 isotope. Therefore carbon is taken reference for the determination of atomic masses.Ītomic mass of an element is the number of times an atom of that element is heavier than an atom of carbon taken as 12. Initially, the atomic masses of all the elements were obtained by comparing with the mass of hydrogen taken as 1 but by doing so, the atomic masses of most of the elements came out to be fractional. So, if oxygen is assigned a value of 200. If the atomic mass of the hydrogen is taken is 1 ,the relative atomic mass of oxygen is 16. In the current system, carbon is exactly 12 and oxygen is approximately 16. The most abundant (99.76 atom percent) isotope of naturally occurring. Thus, though the actual masses of the atoms could not be determined but their relative masses could be determined. Oxygen-16 atom is the stable isotope of oxygen with relative atomic mass 15.994914. Over here, oxygen will be seven 7.936 sodium, probably 22.817 And hes a bloody 11 like and the value from the periodic table is 16 23 and 24 so you can see that its a value for sodium but has wrong values. If equal volumes of two different gases are taken under similar conditions of temperature and pressure and then weighted, the ratio of their masses will be equal to the ratio of their single molecules. The average atomic mass of oxygen is 15.9994 atomic mass units. The problem was finally solved by Avogadro’s hypothesis. The radioisotopes all have half-lives of less than three minutes. Three are stable, 16 O, 17O, and 18O, of which 16 O is the most abundant (over 99.7). amu - atomic mass units O-16 - 15.995 amu O-17 - 16.999 amu O-18 - 17.999 amu the average atomic mass is 15. Oxygen has seventeen known isotopes with atomic masses ranging from 12.03 u to 28.06 u. As an atom is so small a particle that it cannot be seen or isolated ,therefore it is impossible to determine the actual mass of a single atom by weighing it. the average atomic mass of oxygen is the atomic mass with respect to 1/12th the mass of a C-12 atom, related to natural abundance.

Atomic mass of oxygen