describe the concepts of isotopes please fast

Isotopes
Before we leave the subject of atomic structure and the periodic table, we need to examine
one other observation: the existence of atoms of the same element that have different
masses.
For example  the element carbon has six protons in its nucleus giving it an
atomic number of 6. Most carbon atoms also have six neutrons in their nuclei, and because
each proton and each neutron contributes one atomic mass unit (1 amu) to the mass of the
atom, carbon atoms of this kind have a mass number of 12 and are written as 12C.

Although all the nuclei of all atoms of the same element will have the same
number of protons, some atoms of the same element may have different masses
because they have different numbers of neutrons. Such atoms are called
isotopes.
For example, about 1% of the atoms of elemental carbon have nuclei containing 7 neutrons,
and thus have a mass number of 13. Such atoms are written 13C. A tiny fraction of
carbon atoms have 8 neutrons in their nucleus and a mass number of 14. Unlike atoms of
carbon-12 and carbon-13, atoms of carbon-14 are radioactive. The 14C isotope is used in
carbon dating. The three forms of carbon, 12C, 13C, and 14C, are isotopes of one another.
Most atoms of the element hydrogen have one proton in their nucleus and have no neutron.
They have a mass number of 1 and are written 1H. A very small percentage (0.015%)
of the hydrogen atoms that occur naturally, however, have one neutron in their nucleus. These
atoms, called deuterium atoms, have a mass number of 2 and are written 2H. An unstable (and
radioactive) isotope of hydrogen, called tritium (3H), has two neutrons in its nucleus

 

 

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