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Why is the atomic mass number not a whole number?
We can find Atomic Mass and mass number in chemical elements. Atomic mass is about weight of the atom. Mass number is about total of neutrons and protons.
Does the mass number of an element have to be a whole number?
Approximately, yes. But the mass number is an average of the masses of the isotopes of the element, weighted together according to their abundance. This averaging of different whole numbers results in the mass number not being a whole number.
Why is an elements atomic mass not listed as a whole number on the table?
There are two main reasons. The first is that the masses of protons and neutrons are not 1 unit but slightly greater. The mass of an atom is the mass of a whole number of protons, a whole number of neutrons as well as the same number of electrons as protons. Overall, therefore, the mass should be greater than the number of protons and neutrons (electrons have very little mass). But some of the mass is converted to energy which is used to hold the positively charged nucleus together. As a result the mass of carbon12 is an exact whole number and that is the only element for which that is true.The second, and possibly more relevant reason is that most atoms are found in the form of isotopes which have different numbers of neutrons and so different masses. The atomic mass listed for an element is an average of the masses of all these isotopes, weighted together according to their abundance of earth.
What elements atomic mass is 18.99?
Fluorine
Can mass only be a whole number?
No, it cannot. A whole number is a quantity without units - a pure number. A mass of 1 pound is a whole number of pounds but it is 0.45359 kilograms: not a whole number, or 453.59 grams, again not a whole number.
