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Thursday, April 4, 2019

What is isotope ?

What is isotope ?
What is isotope ? - rictasblog

Isotope. Is the set of atoms of the same element that have different mass index and equal atomic number and behave chemically in the same way. They are atoms of the same element, which generally have in their nuclei as well as protons, a number of neutrons that vary their mass, although these do not affect their chemical properties, which is influenced by the amount of protons (positively charged particles). in the nucleus) and by the electrons (negatively charged particles) of its envelope).

Etymology:

The word isotope comes from the word iso meaning equal and mole meaning soil, earth. The etymology refers to the fact that isotopes have the same (iso) atomic number (Z) or number of protons, which is the base or floor (soil) so that the chemical element is the same and does not vary in its main quality that is defined by the nucleus. This refers to the place of order of a certain element in the periodic system, most of the natural chemical elements are not isotopically pure. Tin (Sn), for example, consists of a mixture of 10 different isotopes, while only 22 of the 90 natural elements are made up of a single type of atom, including Helium (He).

History

Studies on the differentiation of the structure of atomic nuclei began together with the twentieth century. The experiments carried out indicated that chemically inseparable radioactive substances could be differentiated only in their nucleus. In 1912, Sir Joseph Thomson, a British physicist, showed that some isotopes are stable. His experience consisted in passing neon (Ne) through a luminous tube and diverting the neon ions through electric and magnetic fields; This showed that neon exists in more than one way. This is how Thomson found two isotopes of Neon Ne-20 and Ne-22. Other experiments showed that the neon existing in nature contains: • 90% neon-20 • 0.27% neon-21 • 73% neon-22 Francis William Aston, British physicist, continued with 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 the deflection or braking was recorded on a photographic plate, and depended on its mass and velocity. The greater the mass of the ion, the lower its deflection. Aston measured the molecular masses of the isotopes of many elements, and verified the relative abundance of them in nature. Most elements in the natural state consist of a mixture of two or more isotopes. Some exceptions are Beryllium (Be), Aluminum (Al), Phosphorus (P) and Sodium (Na) Also today, artificial radioactive isotopes or radioisotopes are developed. They were produced in 1933 by the French 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.

What are the Isotopes?

It is known as an isotope to the varieties of atoms that have the same atomic number and that, therefore, constitute the same element although they have a different mass number. Atoms that are isotopes with each other have the same number of protons in the nucleus and occupy the same place in the periodic table. Most chemical elements have more than one isotope. Only 21 elements, such as sodium, have a single natural isotope. It is possible to divide isotopes into stable isotopes and non-stable or radioactive isotopes. For an isotope to be radioactive, it must exhibit a ratio between the number of protons and neutrons that is not conducive to maintaining nuclear stability. The notion of stability, in any case, is not very precise since there are isotopes that are almost stable thanks to an extremely long neutralization time. The radioactive isotope has an unstable atomic nucleus before the balance between neutrons and protons. This same characteristic makes it emit energy when it mutates in a way towards more stable conditions. The non-stable isotopes have a period of disintegration where the energy is emitted in the form of beta rays (electrons or positrons), alpha (helium nuclei) or gamma (electromagnetic energy). Applications of radioactive isotopes Medicine: In medicine, the high-energy radiation emitted by the radio was used for a long time in the treatment of cancer. Cobalt-60 is currently used to treat cancer because it emits radiation with more energy than the radio emits and is cheaper than this. In medicine, treatment with cobalt-60 is used to stop certain types of cancer based on the ability of gamma rays to destroy cancerous tissues. Cobalt-60 decays by emitting beta particles and gamma rays, and has a half-life of 5.27 years. Its disintegration process is represented by the nuclear chemical equation: 2760Co ----> 2860Ni + -10b + 00g. t 1/2 = 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, treated with sodium iodide (NaI) containing radioactive iodide ions from iodine-131 or iodine-123 There the radiation destroys the cancer cells without affecting the rest of the body. To detect circulatory disorders of the blood a sodium chloride solution (NaCl) containing a small amount of radioactive sodium is used and by measuring the radiation the doctor can know if the circulation of the blood is abnormal. For the study of brain disorders, a proton emission tomography known as PET is used. The patient is given a dose of glucose (C6H12O6) containing a small amount of carbon-11 (11C), which is radioactive and emits positrons, then a scan of the brain to detect the positrons emitted by radioactive glucose "marked " The differences between glucose injected and metabolized by normal and abnormal brains are established. For example, with the PET technique it has been found that the brain of a schizophrenic metabolizes around 20% of the glucose metabolized by a normal individual. Some radioisotopes used in medicine. Chemistry: One of the first applications of radioactive isotopes in chemistry was in the study of the speeds of a reversible reaction to establish equilibrium conditions. For example, to know the equilibrium in a saturated solution of lead chloride II (PbCl2). The chemical equation that represents the equilibrium of this solution is: PbCl2 (S) ----> Pb2 + (ac) + 2 Cl1- (ac) The radioactive isotope of lead-212 is used to verify that the dissolution and precipitation processes occur at the same speed. A small amount of lead II nitrate containing the lead-212 isotope is added to a saturated solution of lead chloride II. Some time later lead is precipitated, indicating that an exchange is taking place between the solid lead chloride and the lead +2 ion of the solution. In studies of organic chemistry, radioactive isotopes are used as tracers or tracers (for example, carbon-14) to know the mechanisms of complex reactions such as photosynthesis, in which more complex molecules are formed in several stages. To study the trajectory of chemical reactions in photosynthesis, the plant is fed carbon dioxide (CO2) containing carbon-14. For this, the American chemist Melvin Calvin (1911) won the Nobel Prize in Chemistry in 1961, clarified a part of the chemical process of photosynthesis and the intermediate products that are produced (Calvin cycle) Dating: Measurements of radioactivity are used to determine the age of minerals and fossil remains (dating). For example, the existence of natural radioactive nuclei on the surface of the Earth suggests that their half-lives are comparable with the ages of the minerals in which they are found, and these provide an estimate of the age of the Earth. How radioactive isotopes are used to determine how long the rocks solidified (age of the rocks) is known as "natural clocks". For example, if a rock contained uranium-238 by solidifying the products of the radioactive decay of uranium can not escape by diffusion, so they are retained in the rock, and become lead-206. To know the half-life (t1 / 2) of the rock, it is necessary to know the overall chemical reaction of the process and the current relationship between lead-206 and uranium-238 in the rock, and it is: 92 238U ----> 82 206Pb + 8 24He + 6 -10e t 1/2 = 4.5x109 years. The disintegration reaction is of the first order, therefore, the equation that relates the concentration and the reaction time is: ln Ci / Cf = kt or log Ci / Cf = kt / 2.3; where Ci is the initial concentration of reagent, Cf is the final concentration of reagent, t is the time it takes for the concentration of the initial reagent to fall, and k is the ratio of the reaction rate between the initial concentration of the reagent and is known as the speed constant. The age of the rocks determined by this method varies between 3x109 years and 4x109 years. The highest value is taken as the approximate age of the Earth (four thousand five hundred million years).

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