How is an element's atomic mass determined?

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Mass is a physical property of matter and is expressed in SI units as kilogram. The atomic mass of elements is not actually the mass of their atoms in kilograms, rather it is a value giving the ratio of the atom's mass to that of the mass of a carbon...

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Mass is a physical property of matter and is expressed in SI units as kilogram. The atomic mass of elements is not actually the mass of their atoms in kilograms, rather it is a value giving the ratio of the atom's mass to that of the mass of a carbon atom which has been fixed at 12 a.m.u (atomic mass unit).

There are three particles that make up an atom, proton, neutron and electron. The mass of protons and neutrons is considered to be equal though in reality neutrons are heavier than protons; the mass of electrons is very less and ignored in the calculation of atomic mass.

An atom of Carbon has 6 protons and 6 neutrons, it is given an atomic mass of 12 a.m.u which makes each proton and neutron in the nucleus of any element contribute 1 a.m.u to the atom's atomic mass.

The number of protons is unique for each element but they can have different numbers of neutrons which leads to elements having isotopes with different atomic mass. The atomic mass of an element is the weighted average of the atomic mass of its isotopes. This requires a knowledge of the relative abundance of each isotope of the element.

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