Atomic mass is calculated by taking into account the masses of the protons, neutrons, and electrons in an atom.
The atomic mass of an element is given as a weighted average of the masses of its isotopes. Isotopes are atoms of the same element that have different numbers of neutrons in their nuclei. The atomic mass of an element is expressed in atomic mass units (amu).
Here's a step-by-step process to calculate the atomic mass of an element:
Determine the isotopic abundance: The first step is to determine the relative abundance of each isotope of the element. This information is usually provided as a percentage or a decimal.
Determine the mass of each isotope: The next step is to find the mass of each isotope. The mass of an isotope is the sum of the masses of its protons, neutrons, and electrons. The masses of protons and neutrons are approximately 1 amu each, while the mass of an electron is negligible compared to protons and neutrons.
Multiply the mass of each isotope by its abundance: Multiply the mass of each isotope by its relative abundance or percentage. This will give you the contribution of each isotope to the total atomic mass.
Sum up the contributions: Add up the contributions of each isotope to get the total atomic mass.
For example, let's calculate the atomic mass of a hypothetical element X:
Isotope X-50 with an abundance of 70% has a mass of 50 amu. Isotope X-52 with an abundance of 30% has a mass of 52 amu.
Atomic mass of X = (0.70 × 50 amu) + (0.30 × 52 amu) = 35 amu + 15.6 amu = 50.6 amu
Therefore, the atomic mass of element X is 50.6 amu.
In reality, atomic masses listed on the periodic table take into account the average atomic mass of all the naturally occurring isotopes of an element, considering their abundances.