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Isotopes are atoms whose atomic 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 has the same atomic number (Z) but each has a different mass number (A). The atomic number corresponds to the number of protons in the atomic nucleus of the atom. The mass number corresponds to the sum of neutrons and protons in the nucleus. This means that different isotopes of the same atom differ from each other only by the number of neutrons.

The elements that can be found in nature can be configured in a wide variety of different isotopes. The mass that appears in the periodic table of the elements is the average of all the masses of all isotopes that can be found naturally.

periodic table of elements

Each atom can have any amount of neutrons. The different combinations of neutrons and protons imply differences in the cohesive forces of the isotope nuclei. Thus, although they may have any number of neutrons there are some combinations of protons and neutrons preferred in the different isotopes.

Light isotopes (with few protons and neutrons) tend to match the amount of neutrons and protons, while heavy isotopes usually have more neutrons than protons.

That each isotope of the same element has the same atomic number means that 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 can have different numbers of neutrons.

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

Unstable isotopes

Usually, what makes an isotope unstable is the large nucleus. If a nucleus becomes large enough from the amount of neutrons it will be unstable and try to expel its neutrons and / or protons to achieve stability. The emission of neutrons / protons, as well as gamma radiation is radioactivity.

Unstable isotopes have many possible applications in our lives. First, a cobalt isotope is used in medicine to stop the spread of cancer. Radioactive isotopes can be used as tracers in patients to monitor various internal processes. An iodine isotope has been used to find brain tumors. In addition to nuclear medicine, in industry, unstable isotopes can measure the thickness of the metal or use them to generate electricity, such as sources of uranium or plutonium.

However, these unstable isotopes can be dangerous in high doses and difficult to store, so it is extremely important to limit or discourage contact with these isotopes completely. Certain isotopes can also have very high energies and release large amounts of nuclear energy when they decompose, creating a potentially destructive hazard.

How are the different isotopes of an element represented?

Uranium is presumed in a wide variety of isotopesThere are two ways to represent them: according to scientific notation and according to symbolic notation.

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

Isotope discovery

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

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

We can classify isotopes as stable, with a half-life of the order of 3 billion years, and unstable or radioactive, which emit radiation and become other isotopes or elements. The latter are used in obtaining electrical energy235 U, 239 Pu) through nuclear fission reactions, in dating ( 14 C, 40 K), in nuclear medicine for diagnostic and therapeutic purposes, in measuring devices, etc.

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Last review: November 28, 2019