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The relative Atomic Mass is defined as: "The weighted mean of the relative isotopic masses of an element on the scale where 12C is 12 amu exactly; symbol Ar." (Heinemann Chemistry 1, 4th Edition).

An atomic mass is always near to the number of Protons and Neutrons within an atom. (12C has a relative atomic mass of exactly 12 amu, but 13C has a relative atomic mass of 13.003 amu for example). Isotopes are Atoms with the same number of protons but different numbers of neutrons. Isotopes used in the calculation of relative atomic mass are naturally formed. The percentage of each type of isotope within a sample of an element is calculated (one way is by using a mass spectrometer). The values are then used to calculate the relative atomic mass.

Example: Calculating hydrogen's relative atomic mass Hydrogen has 3 common isotopes that are naturally formed. 1H (protium), 2H (deuterium), and 3H (tritium). The atomic masses and the percentage of each of these found in a sample is found to be: Atomic Mass % in sample (values may not be exact)

  1. 1H 1.008 amu 99.986%
  2. 2H 2.014 amu 0.014%
  3. 3H 3.016 amu 0.0001%
These are then used to calculate the relative atomic mass as follows ((1.008 amu * 99.986%) + (2.014 amu * 0.014%) + (3.016 amu * 0.0001%)) / 100% Which equals approximately 1.008143856 amu.
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Related Questions

What is the atomic mass on the periodic table?

Each element on the periodic table has two numbers: the atomic number and the relative atomic mass. The atomic number is the number of protons in the nucleus, and the relative atomic mass is the total number of protons and neutrons (so the difference between them is the number of neutrons). The relative atomic mass is always the higher of the two.


The number of an element determines its?

it depends which number you are referring to. in the periodic table, the numbers referr to number of protons and then relative atomic mass. the larger number is relative atomic mass and the smaller number is the number of protons for example, chlorine, has a relative atomic mass of 35.5 and a proton number of 17


Why the relative atomic mass is not a whole number?

Bexause its similar with the atomic mass


Hydrogens atomic mass number and relative atomic mass?

Hydrogen is a non metal element. Atomic mass number of it is 12.


The mass number of an atom can be equal to the atomic number.?

Yes but only if there are no neutrons, such as in hydrogen (atomic number=1, relative Atomic Mass-1)


What is the atomic number and mass of carbon?

Carbon is a non metal element. Atomic number of it is 12.


What do you do with an atomic number and an atomic mass?

The atomic number is the number of a chemical element in the periodic table of Mendeleev; the atomic number is equal to the number of protons and electrons. The atomic mass is the mass of an atom expressed in relative atomic mass units.


What is the number of atomic mass in an atom?

Relative mass number of an electron is 0


What is the Relative atomic mass of chromium?

Chromium is a meta element. Atomic mass of it is 52.


What is the mass number in argon?

The relative atomic mass is 39.95


Atomic mass differnet from the atomic mass number why is that?

The atomic mass is an average, allowing for the relative abundances of different isotopes.


What does the relative atomic mass of an element tell us about the relative abundance of an isotope?

None. The relative abundance of isotopes is used to calculate the Average Mass (by multiplying the Atomic Mass of the isotopes by their relative abundancies and adding the products together) while the Atomic Mass is simply the number of protons plus the number of neutrons.