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Table of Atomic Masses and Carbon Atom Mass

Introduction: The table of atomic masses is a list of the relative masses of atoms based on their isotopic composition and expressed in atomic mass units (amu). The atomic mass of an element is the weighted average of the masses of its isotopes, taking into account their natural abundance. The standard reference for atomic masses is the carbon-12 isotope, which is assigned a mass of exactly 12 amu. However, if we were to use a different reference point, such as oxygen-16, we would obtain different values for the atomic masses of other elements.

Option 1: Carbon mass as 24 amu: If we use oxygen-16 as the reference point and assign it a mass of 200 amu, we would divide this value by the mass of one oxygen atom, which is 16 amu. This gives us a conversion factor of 12.5, meaning that one atomic mass unit would be equal to 12.5/16 or 0.78125 amu. Therefore, the mass of a carbon atom, which has six protons and six neutrons, would be approximately 12 times its atomic number, or 72 amu, when measured relative to oxygen-16. Using the conversion factor, we can express this mass in terms of amu units based on carbon-12, which is the standard atomic mass scale. Dividing 72 by 12.5, we get a mass of 5.76 amu for carbon-12, which is close to its actual mass of 12 amu.

Option 2: Carbon mass as 150 amu: If we use oxygen-16 as the reference point and assign it a mass of 200 amu, we would obtain a different conversion factor of 1.25, meaning that one atomic mass unit would be equal to 1.25/16 or 0.078125 amu. Therefore, the mass of a carbon atom, which has six protons and six neutrons, would be approximately 12 times its atomic number, or 72 amu, when measured relative to oxygen-16. Using the conversion factor, we can express this mass in terms of amu units based on carbon-12, which is the standard atomic mass scale. Multiplying 72 by 0.078125, we get a mass of 5.625 amu for carbon-12, which is less than half of its actual mass of 12 amu.

Conclusion: The choice of reference point for the atomic mass scale affects the numerical values of the masses of all other elements. If we use oxygen-16 as the reference point and assign it a mass of 200 amu, the mass of a carbon atom would be either 24 amu or 150 amu, depending on whether we use the correct conversion factor. However, these values are not consistent with the known mass of carbon-12, which is the basis for the atomic mass scale. Therefore, it is important to use a standardized reference point and conversion factor when comparing atomic masses.

In the current system carbon is exactly 12 and oxygen is approximately 16. Thus carbon has 3/4 the mass of oxygen. So, if oxygen is assigned a value of 200, carbon would be 3/4 of 200 or 150.