What is an Isotope? Definition, Concept and Parts of an Isotope

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  1. Isotope definition
    1. The isotopes. What are they?
    2. Whoever discovered the isotope
    3. Radioactive isotopes
    4. Isotopes in the Periodic Table of Elements
    5. What are isotopes for?
  2. Applications of radioactive isotopes
    1. Medicine
    2. Discovery of isotopes
    3. Neon in nature contains
  3. You may be interested:

Isotope definition

Varieties of atoms that have the same atomic number and therefore constitute the same element, even if they have a different mass number, are known as isotopes. Atoms that are isotopes to each other have identical numbers of protons in the nucleus and are in the same place within the periodic table.


It has its etymological origin in the Greek language and is composed of two parts of that language: isos that can be translated as "equal" and moles that means"place".

The isotopes. What are they?

Isotopes are atoms whose atomic nuclei have the same number of protons but a different number of neutrons.

Not all the 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 of the nucleus. This means that the different isotopes of the same atom differ only in the number of neutrons.

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

Whoever discovered the isotope

His discovery is attributed to the English chemist Frederick Soddy in 1911 who studied the radiation of organic substances in the earth, he realized the equality of the chemical properties of the elements but noting the difference that generated more radioactivity.

Almost all the chemical elements discovered at present possess at least one isotope, some stable and others unstable, all of them leading to the determination of relevant data on matter, such as the age of the earth recently rewritten in 2010 by the scientist John Rudge, who said that due to the decay of the unstable isotopes of hafnium 182 and tungsten 182 the earth has an age of 4470 million ± 1%.

Radioactive isotopes

The radioactive isotope, which has different names such as radioisotope, radionuclide or radioactive nuclide, is one of several species of the same chemical element with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiation in the form of alpha, beta and gamma rays.

Each chemical element has one or more radioactive isotopes. For example, hydrogen, the lightest element, has three isotopes with mass numbers 1, 2 and 3. Only hydrogen-3 (tritium).

However, it's a radioactive isotope, the other two are stable. More than 1,000 radioactive isotopes of the various elements are known. Approximately 50 of these are found in nature.

The rest are produced artificially as direct products of nuclear reactions or indirectly as radioactive offspring of these products.

Radioactive isotopes have many useful applications. In medicine, for example, cobalt-60 is widely used as a source of radiation to stop the development of cancer.

Other radioactive isotopes are used as tracers for diagnostic purposes as well as in research on metabolic processes.

Isotopes in the Periodic Table of Elements

If we look at the periodic table of the elements, we can see that the atoms are accompanied by two numbers, one at the top and one at the bottom.

The number on the bottom is known as the atomic number (the number of protons) and the number on the top is the mass number (the mass of the atom, which is the sum of the number of protons and neutrons of an atom).

From this initial clarification, we can understand the concept of isotopes, which are atoms with the same amount of protons, but with different numbers of neutrons.

In other words, isotopes are atoms of the same chemical element that do not have the same number of protons and neutrons.

Normally, isotopes do not have special names and the only ones that do have specific names are hydrogen isotopes (there are hydrogen isotopes known as protium, others called deuterium and those called tryptium).

What are isotopes for?

There are stable and unstable isotopes. The former is the most abundant in nature and the latter are less abundant and also have a unique property, emitting radiation.

Thus, unstable isotopes are radioactive. Its practical application appears in very diverse fields: in X-rays or in the use of the carbon 14 technique that allows us to know the dating of a fossil, among many other functions.

One concrete application of isotopes to science was that related to trypio (remember that it is one of the isotopes of hydrogen), which made it possible to find out the structure of DNA.

In the pharmaceutical industry, one type of iodine (iodine-123) is a radioactive isotope used in some nuclear medicine tests (e.g. CT scans).

Applications of radioactive isotopes


In medicine, high-energy radiation emitted by the radio was used for a long time in the treatment of cancer.

Cobalt-60 is currently used for cancer treatment because it gives off radiation with more energy than radio waves and is cheaper than radio waves.

In medicine, cobalt-60 treatment is used to stop certain types of cancer based on the ability of gamma rays to destroy cancerous tissue. Cobalt-60 disintegrates by emitting beta particles and gamma rays and has a half-life of 5.27 years.

Certain types of cancer can be treated internally with radioactive isotopes, such as thyroid cancer, such as iodine going to the thyroid gland, is treated with sodium iodide (NaI) containing radioactive iodide ions from iodine-131 or iodine-123. There, the radiation kills the cancer cells without affecting the rest of the body.

A solution of sodium chloride (NaCl) containing a small amount of radioactive sodium is used to detect circulatory disorders of the blood. By measuring the radiation, the doctor can tell if blood circulation is abnormal.

A proton emission tomography (PET) scan known as a PET scan is used to study brain disorders.

Discovery of isotopes

Studies on the differentiation of the structure of atomic nuclei began in the 20th century. The experiments carried out indicated that chemically inseparable radioactive substances could only be differentiated in their nucleus.

In 1912, Sir Joseph Thomson, a British physicist, showed that some isotopes are stable. His experience consisted of passing neon (Ne) through a light tube and deflecting neon ions using electric and magnetic fields.

This showed that neon exists in more than one form. That's how Thomson found two isotopes of the Neon Neon Neon Neon-20 and Neon-22.

Neon in nature contains

  1. 90% neon-20
  2. 0.27% neon-21
  3. 73% neon-22

Francis William Aston, a British physicist, continued the study of isotopes. An instrument called a mass spectrometer helped detect and study isotopes mostly.

This instrument, developed in 1919 by Aston, used a positively charged (+) ion beam, which was first deflected by an electric field and then deflected in the opposite direction by a magnetic field.

The amount of particles resulting from deflection or braking was recorded on a photographic plate, and depended on its mass and speed. The higher the mass of the ion, the lower its deflection.

Aston measured the molecular masses of the isotopes of many elements, and checked the relative abundance of them in nature.

Most elements in their natural state consist of a mixture of two or more isotopes. Some exceptions are Beryllium (Be), Aluminium (Al), Phosphorus (P) and Sodium (Na). Artificial radioactive isotopes or radioisotopes also develop today.

They were produced in 1933 by Frenchmen Irène Curie and Frédéric Joliot-Curie. Radioisotopes are obtained by bombarding existing atoms in nature with nuclear particles such as neutrons, electrons, protons and alpha particles, using particle accelerators.

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