Q:

# Why isn't the atomic mass usually a whole number?

A:

The atomic mass is not given as a whole number because it is a weighted average taken of all of an atom's isotopes found in nature relative to the mass of carbon-12. The measurement unit used for atomic mass is the unified atomic mass that has the symbol "u." This is a derived unit from the carbon-12 isotope, where 12 u is the atomic mass of carbon-12.

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On the periodic table, students can find the atomic mass written below the element's name. The number written above the element is the atomic number, which is the number of protons of a given element. For example, lithium has an atomic mass of 6.941 and an atomic number of 3.

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## Related Questions

• A:

Carbon's atomic number is 6, and its atomic mass is 12.0107 atomic mass units. The atomic number defines the number of protons located in the atom's nucleus, so carbon has six protons. Each element has its own atomic number.

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• A:

The atomic number of an atom is the number of protons that resides in the nucleus, while the mass number is the number of protons and neutrons combined. The atomic number determines the type of element an atom, while the number of neutrons determines the isotope of the element. Many elements naturally occur in the form of several different isotopes.

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• A:

The molar mass of calcium is 40.07 grams per mole, which is the same as the atomic mass of the element. The molar mass is found by determining the mass of a substance present in a single mole.