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Explain why relative atomic masses are rarely whole numbers. - Leaving Cert Chemistry - Question (b) - 2015
Question (b)
Explain why relative atomic masses are rarely whole numbers.
Worked Solution & Example Answer:Explain why relative atomic masses are rarely whole numbers. - Leaving Cert Chemistry - Question (b) - 2015
Step 1
average mass of isotopes of an element
Answer
The relative atomic mass of an element is not simply the whole number of a single isotope due to the presence of multiple isotopes. Each isotope has a different mass number, defined as the sum of protons and neutrons in the nucleus. The relative atomic mass reflects the average of these isotopic masses, weighted by their natural abundance. Therefore, it results in a non-whole number since it considers the contribution of each isotope proportionally.
Step 2
average mass of all atoms of an element
Answer
Moreover, the average mass does not correspond directly to whole numbers because of the existence of subatomic particles. The masses of protons and neutrons are not precisely whole numbers either, primarily because they are measured in atomic mass units (amu) where fractional values are common due to the binding energy associated with the strong nuclear force. Consequently, when these particle masses are averaged based on isotopic composition, it further leads to relative atomic masses that rarely align as whole numbers.
Step 3
subatomic particles' masses
Answer
Additionally, the varying masses of protons and neutrons contribute to this discrepancy. For example, while the mass of a proton is approximately 1.0073 amu and a neutron approximately 1.0087 amu, their combined effect in atomic structure leads to average atomic mass values that are not whole, hence accounting for the rarity of whole number relative atomic masses.