To find the atomic mass of an element, follow these key points:

• The atomic mass (or atomic weight) is essentially the weighted average mass of all the isotopes of that element, measured in atomic mass units (amu).
• For a single atom, the atomic mass is approximately the sum of the number of protons (atomic number) and neutrons in its nucleus, also called the mass number.
  Formula:

Mass number=Number of protons+Number of neutrons\text{Mass number}=\text{Number of protons}+\text{Number of neutrons}Mass number=Number of protons+Number of neutrons

• Since elements exist as mixtures of isotopes with different numbers of neutrons, atomic mass represents an average that accounts for the relative abundance of each isotope. This is why atomic mass values on the periodic table are often not whole numbers.
• To calculate the average atomic mass, multiply the mass of each isotope by its fractional abundance, then sum these values.
• Numerically:

Average atomic mass=∑(isotope mass×fractional abundance)\text{Average atomic mass}=\sum (\text{isotope mass}\times \text{fractional abundance})Average atomic mass=∑(isotope mass×fractional abundance)

In simple terms, you find either the mass number of a specific isotope by adding protons and neutrons or find the atomic mass by averaging the masses of all isotopes based on how common they are in nature. For example, helium has 2 protons and 2 neutrons, so its mass number is 4, and the atomic mass is close to that value. When multiple isotopes exist with different neutron counts, the atomic mass reflects an average weighted by isotope abundance.

Let me know if a specific calculation or example is needed.