carbon- 12 weighs exactly 12 atomic mass units
Dmitri Mendeleev and Lothar Mayer (independently).
I can find only two types The Mendeleves Periodic table based on Atomic weight of elements and The Modern Periodic table based on Atomic number of elements.
Atomic percent is based on the number of atoms in a sample. So if the sample has x number of oxygen atoms and x number of iron atoms it would report 50% oxygen and 50% iron (atomic percent). Weight percent is based on the mass of the elements detected. So if we used the above example and reported the results as weight percent we would get 22.3% oxygen and 77.7% iron. Weight percent takes into consideration the mass or atomic weight of the elements and not just the number of atoms. Most people use weight percent although for chemistry atomic percent may be more useful.
Atomic mass minus atomic number will give you the average number of neutrons in that element. Bear in mind that atomic mass is based on the actual weight of that element, which is the result of whatever isotopes appear in nature; it is rarely based on only a single isotope.
No, it is based upon the Atomic Number - the number of protons contained within an atomic nucleus is what 'distinguishes' one type of Atom from another type. Variations in atomic mass are secondary in consideration.
Atomic weight.
In 1914 Henry Moseley found a relationship between an element's X-ray wavelength and its atomic number (Z), and therefore rearranged the table by nuclear charge / atomic number rather than atomic weight. Before this discovery, atomic numbers were just sequential numbers based on an element's atomic weight. Moseley's discovery showed that atomic numbers had an experimentally measurable basis.
Carbon 12 isotope weighs exactly 12 atomic mass units thank you the other person who said it was B is a douche
It is based on number of protons. Consider an element has 20 protons.Its atomic number is twenty.
1914. In 1914 Henry Moseley found a relationship between an element's X-ray wavelength and its atomic number (Z), and therefore resequenced the table by nuclear charge rather than atomic weight. Before this discovery, atomic numbers were just sequential numbers based on an element's atomic weight. Moseley's discovery showed that atomic numbers had an experimentally measurable basis.
In 1914 Henry Moseley found a relationship between an element's X-ray wavelength and its atomic number (Z), and therefore resequenced the table by nuclear charge rather than atomic weight. Before this discovery, atomic numbers were just sequential numbers based on an element's atomic weight. Moseley's discovery showed that atomic numbers had an experimentally measurable basis.