Molecular Structure.
Atoms, electrons, neutrons and protons

Isotopes, what are they?

Isotopes, what are they?

Isotopes are atoms whose nuclei have the same number of protons but different numbers of neutrons. Not all atoms of the same element are identical and each of these varieties corresponds to a different isotope.

Each isotope of the same element have the same atomic number (Z) but each has a different mass number (A). The atomic number is the number of protons in the atomic nucleus of the atom. The mass number is the sum of neutrons and protons of the core. This means that different isotopes of the same atom differ from each other only by the number of neutrons.

The items that can be found in nature can be configured in a variety of different isotopes. The mass shown on the periodic table is the average of all the masses of all the isotopes that can be found naturally.

periodic table of elements

Each atom can have any number of neutrons. Different combinations of neutrons and protons involve differences in the cohesion forces of the nuclei of isotopes. Thus, although they can have any number of neutrons there are some combinations of protons and neutrons preferred in isotopes.

The light isotopes (with few protons and neutrons) use to have the same amount of neutrons and protons, while heavy isotopes often have more neutrons than protons.

The fact that each isotope of an element have the same atomic number means they have the same number of protons in the atomic nucleus. Atoms of the same element have the same number of protons and electrons but may have different numbers of neutrons.

Isotopes can be found with excess or lack of neutrons. These atoms can exist for some time, but are unstable. Unstable atoms are radioactive: their nuclei change or decay by emitting radiation.

How different isotopes of an element are represented?

Prestenta uranium in a variety of isotopes There are two ways of representing: according to scientific notation and according to symbolic notation.

  • Scientific notation isotopes: isotopes are identified by the name followed by the number of protons and neutrons in the isotope chemical element. For example, the three most common isotope in the uranium (used as nuclear fuel) are represented like: U-235, U-235 and U-238
  • Symbolic notation isotopes: the number of nucleons (protons and neutrons) is denoted as superscript prefix chemical symbol. In the case of the above three isotopes of uranium would 234U, 235U and 238U

Discovery of isotopes

The existence of isotopes was discovered as a result of the study of natural radioactive substances. The name isotope was proposed by F.Soddy in 1911. Soddy found the equality of its chemical properties.

Most of the elements are formed by several isotopes that can only be separated by physical methods (diffusion, centrifugation, mass spectrometry, fractional distillation and electrolysis).

We can classify as stable isotopes (isotopes with a life of about three thousand million years), and unstable or radioactive. Unstable isotopes emit radiation and become other isotopes or elements. Additionally, unestable isotopes are used in the production of electricity (235U, 239Pu) by nuclear fission reactions, in dating (14C, 40K), in nuclear medicine for diagnostic and therapeutic purposes, measuring instruments, etc.

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Last review: November 2, 2016