Different nuclei of the same element having the same number of protons and different neutron numbers are Isotopes.

Isotopes Definition

The atom in the above definition is a generalized concept, referring to microscopic particles. Different nuclei of the same element having the same number of protons and different numbers of neutrons are called Isotopes.


For example, hydrogen has three isotopes (also called heavy hydrogen). Carbon has multiple isotopes, 12 C, 13 C and 14 C (with radioactivity).

Isotopes are different atoms of the same element, and their atoms have the same number of protons, but the number of neutrons is different.

For example Protium, deuterium, and tritium, which nuclei in both a proton, but their nuclei respectively were 0 neutrons, a neutron, and two neutrons, so that they are each isotope. Wherein, the relative atomic mass of Protium 1.007947, the relative atomic mass of deuterium is 2.274246, the relative atomic mass of 3.023548 tritiums, deuterium almost twice heavier than protium, tritium and protium ratio is almost twice as heavy.

Isotopes having the same atomic number identical chemical element of two or more atoms in the periodic table occupies the same position, almost the same (chemical nature protiumdeuterium and tritium properties slightly different), but an atomic mass or mass The number is different, so that its mass spectrometry properties, radioactive transitions, and physical properties (such as diffusion in the gaseous state) vary. The isotope is indicated by the mass number in the upper left corner of the element symbol (eg carbon 14, generally indicated by 14 C).

Here are some other Articles that you will Probably Enjoy-

Naturally occurring isotopes in nature are called natural isotopes, and synthetic isotopes are called artificial isotopes. If the isotope is radioactive, it will be called a Radioisotope. Each element has a Radioisotope. Some radioisotopes are found in nature, while others are artificially produced by bombarding stable nuclei with nuclear particles such as protons, particles or neutrons.

Basic nature of Isotopes

Isotopes having the same atomic two or more atoms of the same ordinal number of the chemical element in the periodic table occupies the same position, almost the same chemical behavior, but an atomic mass or mass number different, thus the mass behavior, radioactive transformation, and physical Properties (such as diffusion in the gaseous state ) vary.


The isotope is indicated by the mass number (proton number + neutron number) in the upper left corner of the element symbol and the proton number in the lower left corner. For example, carbon 14, generally 14 C instead of C-14.

Many elements in nature have isotopes. Some isotopes are naturally occurring, some are artificially manufactured, some are radioactive, and some are not radioactive.

Although the isotopes of the same element have different masses, their chemical properties are basically the same (such as chemical reactions and ion formation), and physical properties are different [mainly in terms of mass (eg, melting point and boiling point)]. In nature, the percentage of atoms of various isotopes is constant.

Isotopes refer to atoms (nuclides) that have the same nuclear charge but different atomic masses. At the end of the 19th century, radioisotopes were first discovered, followed by naturally occurring stable isotopes, and the abundance of isotopes was determined. There are several stable isotopes in most natural elements. The isotopic qualities of the same elements are different, but the chemical properties are almost the same.

Since the discovery of radioactivity at the end of the 19th century, more than 30 radioactive elements have been discovered by the early 20th century, and it has been shown that some radioactive elements, although significantly different in radioactivity, are chemically identical.

Development application


Many isotopes have important uses, such as C-12 as an atom for determining atomic weight standards; two H atoms are materials for making hydrogen bombs; U-235 is a material for making atomic bombs and a raw material for nuclear reactors.

Isotope tracer is widely used in scientific research (such as national defense), industrial and agricultural production, and medical technology. For example, the process of esterification is confirmed by O- labeled compounds, and I is used for experiments on thyroid iodine absorption.

Here are some other Articles that you will Probably Enjoy-

Peaceful use of nuclear energy

Important aspects of the peaceful use of nuclear energy are also an important part of the nuclear industry’s service to the national economy and people’s lives.

In 1982, the Ministry of Nuclear Industry established the China Isotope Company, which is responsible for organizing isotope production, supply and import and export trade has established 19 branches including nuclear agronomy, nuclear medicine, nuclear power, radiation technology, and isotope. Various professional conferences have been held to promote the application of nuclear energy, isotopes, and other nuclear technologies.

There are more and more varieties of isotope energy produced in China, including radiopharmaceuticals, various radioactive sources, labeled compounds such as hydrogen-3 and carbon-14, radiochemical preparations and various kits for radioimmunoassay and stable isotopes and their markers. Compounds, etc.

The isotope production unit in China Institute of Atomic Energy isotope production accounted for more than 80% of the national total. China’s isotope users in the country, relying mainly on imports from the past, gradually turned to mostly self-sufficiency in domestic production.

With the development of isotope production, the application of isotopes and other nuclear technologies in many sectors has been further promoted, and significant economic and social benefits have been achieved.

Agricultural aspect

In agriculture, the use of radiation methods or radiation and other methods combined to cultivate excellent varieties of crops, so that grain, cotton, soybeans and other crops have achieved a large increase in production.


The use of isotope tracer technology to study the rational use of pesticides and fertilizers and soil improvement has provided new measures for agricultural production. Other research work such as radiation-preserved foods has also made great progress.

Medical aspect

In terms of medicine, there are thousands of medical units across the country, and more than one hundred isotope treatment methods have been established in the clinic, including external irradiation treatment, and in vivo drug irradiation treatment.

Isotopes also play an important role in immunology, molecular biology, genetic engineering research, and the development of basic nuclear medicine.

The study

In 1910, the British chemist F. Soddy proposed a hypothesis that chemical elements have different physicochemical properties that differ in atomic mass and radioactivity. These variants should be in the same position on the periodic table, called isotopes.

Soon, the relative atomic mass of a lead obtained from different radioactive elements (uranium and thorium) was 206.08, and the other was 208. In 1897, British physicist JJ Thomson (Joseph John Thomson) discovered in 1912, he improved the instrument for measuring electrons and made a magnetic separator (predecessor of the mass spectrometer) by using a magnetic field.


When he measured with helium, no matter how it was purified, two parabolas were obtained on the screen, one representing the mass of 20 and the other representing the mass of 22.

This is the first stable isotope discovered, that is, a radioactive isotope. When FW Aston made the first mass spectrometer, it was further proved that helium did have two isotopes with different atomic masses and more than 200 isotopes were found from more than 70 other elements.

So far, 109 elements have been discovered, and only 20 elements have not found stable isotopes, but all elements have radioisotopes. Most of the natural elements are a mixture of several isotopes, with more than 300 stable isotopes and more than 2,800 radioisotopes.

After the proton theory of the nucleus was proposed in 1932, it was further clarified that the isotope is an element in which several atoms with the same number of protons and different numbers of neutrons exist.

For the same number of protons, so that their outer nuclear and nuclear charge number of electrons is the same (number of protons = nuclear charge = extranuclear number), and have the same electron shell structure.

Here are some other Articles that you will Probably Enjoy-

Therefore, the chemical properties of isotopes are the same, but because of their different neutron numbers, this causes the quality of each atom to be different, and some physical properties (such as radioactivity) involving the nucleus are also different.

In general, an element with an even number of protons may have more stable isotopes, and usually, no less than three, while an element with an odd number of protons generally has only one stable nuclide, and its stable isotope never exceeds Two, this is determined by the binding energy of the nucleus.