The atomic mass of helium is not something you typically calculate but rather is experimentally determined and reported on the periodic table; for helium, it is 4.002602 atomic mass units (amu).
Here's a breakdown to clarify:
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Atomic Mass vs. Mass Number: It's important to distinguish between atomic mass and mass number. The mass number is the total number of protons and neutrons in an atom's nucleus (a whole number). The atomic mass is a more precise measurement, reflecting the actual mass of an atom of a specific element, taking into account the masses of protons, neutrons, and electrons, as well as the binding energy of the nucleus.
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Helium's Atomic Mass: The atomic mass of helium (4.002602 amu) is determined experimentally through mass spectrometry and other techniques. It's a weighted average of the masses of all the naturally occurring isotopes of helium, considering their relative abundance. The most common isotope is helium-4.
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Helium Isotopes: Helium primarily exists as helium-4 (4He), which has 2 protons and 2 neutrons. There are also trace amounts of helium-3 (3He). The atomic mass considers the abundance of both isotopes. Since helium-4 is overwhelmingly more abundant, the atomic mass is very close to 4.
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Using the Periodic Table: You can simply find the atomic mass of helium on the periodic table. It's usually listed below the element symbol (He).
In summary, you don't calculate the atomic mass of helium; you find it on the periodic table or in a reliable chemistry reference source. The value represents the experimentally determined average mass of helium atoms in their natural isotopic abundance.
