Discovery of Isotopes

Isotopes are two or more groups of atoms with the same atomic number and periodic table location but different nucleon numbers due to different numbers of neutrons. Although all isotopes of the same element have almost identical chemical properties, their atomic masses and physical properties vary.

Example of Isotope

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This article will study the discovery of isotopes, who discovered the isotopes and how did the discovery of isotopes affect the periodic table in detail.

How Did the Discovery of Isotopes Affect the Periodic Table?

The atomic number is the number of protons in the nucleus of an atom, which is equal to the number of electrons in a neutral (non-ionized) atom. Each atomic number defines a particular element, but not an isotope; the number of neutrons in an atom of a given element may vary widely. The mass number of an atom is determined by the number of nucleons (both protons and neutrons) in its nucleus, and each isotope of a given element has a different mass number.

Carbon-12, carbon-13, and carbon-14, for example, are three carbon isotopes with mass numbers of 12, 13, and 14, respectively. Carbon with an atomic number of 6, which means that every carbon atom has 6 protons, giving these isotopes neutron numbers of 6, 7, and 8, respectively.

Who Discovered the Isotope?

The radiochemist Frederick Soddy was the one who discovered the isotopes. In 1913, based on observations of radioactive decay chains that revealed about 40 different species referred to as radioelements (i.e. radioactive elements) between uranium and lead, despite the periodic table only allowing for 11 elements between lead and uranium inclusive.

T. W. Richards discovered differences in the atomic weight of lead from various mineral sources in 1914, which he attributed to differences in isotopic composition caused by different radioactive origins.

The Discovery of Isotopes

• The discovery of isotopes was based on two separate lines of inquiry, the first of which was the observation of radioactivity. By 1910, it was clear that certain radioactive processes, discovered a few years before by French physicist Henri Becquerel, could change one element into another. Tiny quantities of certain radioactive substances never seen before were found in ores of the radioactive elements uranium and thorium, in particular. These compounds were considered to be elements and were given unique names as a result. Ionium was produced by uranium ores, and mesothorium was produced by thorium ores.

• Chemists were forced to conclude that ionium and mesothorium were not new elements at all, but rather new versions of old ones since the criterion of chemical indistinguishability was part of the concept of an element. In 1910, English chemist Frederick Soddy observed, based on these and other results, that “elements of different atomic weights [now called atomic masses] can possess identical (chemical) properties” and thus belong in the same position in the periodic table. He expanded the spectrum of his conclusion to include not only radioactive organisms but also stable elements, demonstrating his foresight.

• Since uranium and thorium decay into separate lead isotopes, he expected a difference. The average atomic mass of the lead from the uranium-rich mine was 206.08, compared to 207.69 for the lead from the thorium-rich ore, confirming Soddy's conclusion.

Types of Isotopes

• Isotopes are classified as stable or radioactive. As a result, radioactive isotopes are sometimes referred to as radioisotopes or radionuclides.

• Stable isotopes or stable nuclides are isotopes that do not decay radioactively.

• According to the observations, the planet Earth contains approximately 339 naturally occurring nuclides or isotopes.

• 286 of these are said to be primordial nuclides, which are thought to have existed before the Solar System's inception.

Applications of Isotopes 

Use of Chemical Properties

• Isotope analysis is the process of determining an element's isotopic signature, or the relative abundances of its isotopes in a given sample. Isotope ratio mass spectrometry is commonly used for isotope analysis. Significant differences in C, N, and O isotopes may occur in biogenic substances in particular. The use of isoscapes to analyse such variations has a wide range of applications, including detecting adulteration in food products and determining the geographic source of products. The isotopic signature of trace gases found in some meteorites has been used to identify them as having originated on Mars.

• The kinetic isotope effect can be used to determine the cause of a chemical reaction using isotopic substitution.

• The isotope dilution process, in which known quantities of isotopically-substituted compounds are combined with samples and the isotopic signatures of the resulting mixtures are calculated with mass spectrometry, is widely used to calculate the concentration of various elements or substances.

Use of Nuclear Properties 

• Radiometric dating is a method close to radioisotopic labelling in that it uses the observed half-life of an unstable element to measure the amount of time since a known concentration of isotope existed. Radiocarbon dating, which is used to assess the age of carbonaceous materials, is the most well-known example.

• Several types of spectroscopy depend on the unique nuclear properties of radioactive and stable isotopes. Nuclear magnetic resonance (NMR) spectroscopy, for example, can only be used on isotopes with a non zero nuclear spin.

• Radionuclides have a variety of applications. Specific isotopes are required in relatively large quantities for nuclear power and nuclear weapons production. Radioisotopes are used in nuclear medicine and radiation oncology for medical diagnosis and treatment.

Henri Becquerel

Henri Becquerel, full name Antoine-Henri Becquerel, was a French physicist who discovered radioactivity through his studies of uranium and other substances. He was born on December 15, 1852, in Paris, France, and died on August 25, 1908, in Le Croisic. In 1903, he and Pierre and Marie Curie shared the Nobel Prize in Physics.

His grandfather, Antoine-César Becquerel (1788–1878), father, Alexandre-Edmond Becquerel (1820–91), and son, Jean Becquerel (1878–1953), were all members of a scientific family that spanned several generations.

Did You Know?

Isobars are atoms (nuclides) with the same number of nucleons from different chemical elements. Isobars, on the other hand, have different atomic numbers (or protons) but the same mass number. The isobars 40S, 40Cl, and 40Ca are an example of a sequence of isobars. Although all of these nuclides have 40 nucleons, the number of protons and neutrons in their nuclei varies.

Alfred Walter Stewart proposed the name "isobars" (originally "isobares") for nuclides in 1918. It comes from the Greek words isos, which means "equal," and baros, which means "weight."