How The Structure Of Matter Is Associated With Radioactivity

We know that the matter is made up of elements. The smallest part of any element is its atom. Atoms are composed of a positively charged nucleus containing protons (positively charged subatomic particles) and neutrons (inert particles), and around the nucleus, there are orbital electrons (negatively charged subatomic particles). In 1896 Bacquerel discovered the phenomenon of radioactivity in the atoms of some elements. The mass of an atom is represented by its nucleus that is the sum of protons (positively charged subatomic particles) and neutrons (inert particles) in the nucleus. Each element has been allotted a chemical symbol and its atomic number is fixed. The number of electrons is always equal to the number of protons in the nucleus of an atom and this number stands for the atomic number of an atom. Mass of an electron is ¹/₁₈₀₀ of the mass of a proton on atomic scale. The atoms in some of the elements have natural variation in mass number and that made them unstable or radioactive.

Isotopes: Atoms of a particular element not have to be exactly alike in terms of mass number. In such atoms the things that must be alike are the number of protons (positively charged subatomic particles) in the nucleus or the nuclear charge and the number of orbital electrons (negatively charged subatomic particles). But the number of neutrons (inert particles) may vary and hence atomic mass may vary in a narrow range. Atoms of the same element with same atomic number but with different number of neutrons (inert particles) are called isotopes. A single chemical symbol of an element is not sufficient to represent an isotope. The chemical symbol along with a superscript at the upper left or right, depicting the mass number and lower left depicting the atomic number, represents an isotope; however, it is not necessary to mention atomic number to depict an isotope, as ⁵¹Cr represents an isotope of Chromium. Each element has a unique atomic number but the mass number may vary depending on the number of the isotopes of that element. An element generally has only one stable isotope.

Radioactivity: Majority of the elements found naturally have stable atoms. The atoms of the elements never change unless they are attacked with subatomic particles from outside; however, some of the atoms in some heavy elements are inherently unstable. The unstable atoms are called radioactive isotopes or radioisotopes. The nucleus of the radioactive atom or radioisotope undergoes disintegration with the ejection of tiny particle accompanied by electromagnetic radiation. After disintegration the rest of the material of the nucleus rearranges itself and becomes the nucleus of a different element.