The atomic mass of an atom is determined by adding up the masses of its protons and neutrons, which are found in the nucleus. Electrons, on the other hand, have negligible mass compared to protons and neutrons, so they are not considered in the calculation.
The mass of protons and neutrons is measured in atomic mass units (amu). One amu is defined as one-twelfth the mass of a carbon-12 atom. By comparing the mass of protons and neutrons to the mass of carbon-12, scientists can determine the relative mass of each particle.
To calculate the atomic mass, scientists consider the abundance of each isotope of an element and their corresponding masses. Isotopes are atoms of the same element that have different numbers of neutrons.
For example, carbon has two major isotopes: carbon-12 and carbon-13. Carbon-12 is more abundant, with about 98.89% natural abundance, while carbon-13 has a natural abundance of about 1.11%. Scientists assign a relative mass to each isotope, which is calculated based on the amu scale. For carbon, the atomic mass is weighted average of the masses of carbon-12 and carbon-13, taking into account their natural abundances.
In summary, the atomic mass of an atom is determined by adding up the masses of protons and neutrons in the nucleus, considering the natural abundance of each isotope. Electrons, due to their negligible mass, do not significantly contribute to the atomic mass and are not included in the calculation.
How is the atomic mass of an atom determined and why are electrons not used in the calculation?
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