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The relative atomic mass is calculated by the sum of (isotope abundance x isotope mass number) for all the isotopes.
Relative atomic mass, often referred to as atomic weight, is a dimensionless physical quantity defined as the average mass of atoms of an element. It is calculated based on the relative abundance of different isotopes of that element. The formula for calculating relative atomic mass is the sum of the product of the isotope abundance and the isotope mass number for all the isotopes of the element.
To understand this better, let's break it down. An isotope is a variant of a particular chemical element, which means although they are the same element, they have different numbers of neutrons and hence different mass numbers. The isotope abundance is the amount or percentage of each isotope found naturally in a sample of the element. The isotope mass number is the total number of protons and neutrons in the nucleus of an isotope.
So, to calculate the relative atomic mass of an element, you multiply the isotope abundance of each isotope by its mass number, then add up these products. This gives you a weighted average, which takes into account not just the mass numbers of the isotopes, but also how common they are.
For example, chlorine has two main isotopes, Cl-35 and Cl-37. If we assume that 75% of chlorine atoms are Cl-35 and 25% are Cl-37, the relative atomic mass would be (0.75 x 35) + (0.25 x 37) = 35.5. This means that on average, a chlorine atom will have a mass close to 35.5 atomic mass units.
Remember, the relative atomic mass is a dimensionless quantity. This means it has no units because it is a comparison or ratio of the average mass of one atom of an element to one twelfth of the mass of an atom of carbon-12.
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