mass
38. The atoms of all isotopes of any one element have the same number of
protons. This number is called the atomic number and is a characteristic of
the element The nuclei of the different isotopes differ in the number of
neutrons. The ATOMIC MASS NUMBER is the sum of the protons and
neutrons of the nucleus. Atoms of the different isotopic forms are
distinguished by using the mass number as a superscript to the atomic
symbol. Thus, C12 refers to the carbon isotope of mass number 12.
The mass number of an atom is the sum of the _____________________
and the _____________ of the nucleus.
Protons
39. The masses of the individual atoms are very small, the greatest being
neutrons
involving atomic masses, the atomic mass unit (AMU) was adopted. The
atomic mass unit is equal to one-twelfth the mass of a carbon atom. (C12 is
used for this reference, because it is the most abundant carbon isotope.)
According to this standard, the carbon atom has a mass of 12 atomic mass
units.
IT0341
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