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Today we know more than 100 elements with different chemical and physical properties. Initially all known elements were classified as metals and non-metals on the basis of their physical characteristics but later as new elements discovered, this classification was not enough to classify them.

To classify elements, many classifications were given based on atomic weight but as the number of elements increased all were failed. Today we have the Modern form of periodic table which is based on atomic number of all known elements.

This periodic table is based on the concept that chemical and physical properties of elements are periodic function of their atomic number. That is the reason when we arrange elements in increasing order of their atomic number their exhibit periodicity in their properties. The lone form of periodic table is a tabular arrangement is a tabular form with 18 columns, also known as groups and 7 rows called as periods. There are two series of elements at the bottom of main body of periodic table which are commonly called as f-block elements. These elements are radioactive or synthetic elements whish show different chemical and physical properties. 

Can we say that the long form of periodic table does not have any limitation? No! It has few. Since the periodic table is based on atomic number so there was no separate position for isotopes of same elements. Isotopes are different forms of same elements which have same atomic number but different mass number due to different number of neutrons. Since they have same atomic number therefore they are placed at the same position in the periodic table. Because of the presence of different number of neutrons, mass number differs in different isotopes that affect the physical properties of isotopes. For example, there are three isotopes of carbon atoms; C-12, C-13 and C-14. 

Isotopes of Carbon

All these three isotopes have same number of protons (same atomic number) but different number of neutrons. Out of these three isotopes; C-12 and C-13 are stable isotopes whereas C-14 is unstable one. 

Another ambiguity with long form of periodic table is position of hydrogen atom. According to atomic number, hydrogen is placed in group-1 of periodic table. Even hydrogen exhibits similarity with alkali metals also like one valence electron but at the same time it also exhibits some similarity with halogens which are placed in group-17 of periodic table. So we can say that the position of hydrogen is not sure and that is the reason, in some periodic tables you may find it at the top of main body of table.


Tritium Definition

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Hydrogen atom can exist in three isotopic forms; protium, deuterium and tritium. Like other elements, these isotopes are also placed at same position in the periodic table as they have same atomic number but different mass number. 

Isotopes of Hydrogen
Protium is most common isotopes of hydrogen atom with one electron and one proton in it.  Therefore mass number of protium is 1 and atomic number is also one. The atomic representation of protium is H-1 or 1H1.  It is also called as ordinary hydrogen. It has tendency to share its one electron to form one covalent bond with other atom to form molecule. Water is a compound formed by combination of two hydrogen atoms with one oxygen atom. 

Another isotope of hydrogen is deuterium which contains 1 proton and 1 neutron in its nucleus along with 1 electron. That is the reason, mass number of deuterium is 2 and atomic number is 1. Unlike protium, the natural abundance of deuterium is very less around 0.0026 % compare to protium which is 99.98 %.  It is also symbolized as H-2 or 1H2 or heavy hydrogen. 

The least abundant isotope of hydrogen is tritium. It contains 1 proton along with 2 neutrons in its nucleus. That is why mass number of tritium is 3 and it is symbolized as 1H3 or H-3. The atomic mass of tritium is 3.0160492 u and natural abundance is negligible. It is a radioactive isotope of hydrogen which is also found in trace amount in atmosphere due to interaction of cosmic rays.

Another production method of tritium is irradiation of Li nucleus in nuclear reactors. Half life of tritium is 12.32 years and it decays to He-3 nuclei with an electron, an undetectable electron antineutrino and 18.6 keV of energy. 

$31T \rightarrow 32He +  e−  +  νe$

Some other properties of tritium are listed below.

 Properties   Tritium 
 Natural abundance  A trillionth 
 Specific activity  9.800 Ci/g
 Decay mode  Î² (Beta particles)
 Radiation energy  0.0057 MeV
 Spin  $\frac{1}{2}$
 Binding energy  8,481.821 keV
 Decay energy  0.018590 MeV

Naturally this isotope of hydrogen is present in water and water vapor but in trace amount. It is produced in atmosphere due to cosmic rays and is incorporated into water which falls to earth as rain. This process makes it part of natural hydrological cycle. It is one of the fission products of nuclear fission reactions in nuclear weapons tests and in nuclear power reactors.

Tritium Oxide

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We are familiar with water which is an oxide of ordinary hydrogen. The molecular formula of water is H2O that consists of two hydrogen atoms and one oxygen atom. Both hydrogen atoms are bonded through covalent bond with oxygen atom. 

Water Molecule

Similarly deuterium also forms oxide with oxygen which is called as deuterium oxide or heavy water. It is used as nuclear moderator in nuclear reactors to slow down the speed of neutrons. Tritium a radioactive isotope of hydrogen is produced by cosmic rays with below nuclear reactions:

$^{14}N + ^{1}n \rightarrow ^{3}H + ^{12}C$
$^{2}H + ^{2}H \rightarrow ^{3}H + ^{1}H$

The interaction of cosmic rays with nitrogen (14N) or with deuterium (2H) results the formation of tritium and carbon (12C). Bombardment of neutrons on hydrogen atom is one of the laboratory methods of production of tritium. Tritium is unstable due to presence of extra neutrons in nucleus which gives an excess amount of energy and responsible for its decay. Nuclear transformation of tritium atom emits a beta particle (ß-) and an anti-neutrino.

$3H \rightarrow ^{3}He + \beta- + anti-neutrino$

It reduces the energy level and forms a helium atom (3He), is left more stable. 

Oxide of tritium is known as tritium oxide with formula $T_{2}O$ like $H_{2}O$. It is also called as super-heavy water or tritiated water.  It is a radioactive form of water which contains radioactive tritium isotope of hydrogen in place of protium. Pure form of tritium oxide is a corrosive compound which can show self radiolysis. The systematic IUPAC name of tritium oxide is 3H2 and chemical formula is given below. 


Physical State of Tritium Oxide

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The radioactive isotope of hydrogen is tritium with 2 neutrons and 1 proton in its nucleus. The mass number of tritium is 3 and it is represented as T or H-3. Atomic mass of tritium is 3.0160492 u. No doubt the natural abundance of tritium is very less compare to other two isotopes, although it is part of our nature. A trace amount of tritium is present water in the form of $T_{2}O$. Here $T_{2}O$ is tritium oxide which is an oxide like $D_{2}O$ and $H_{2}O$. 

Tritium oxide can be taken into the body from the lungs and can circulate in blood which distributes it in all tissues. It can also completely absorb from the gastrointestinal tract to the bloodstream and reached to body fluids, organs, and other tissues. 

Tritium oxide can also absorb by skin due to exposure with high concentrations of tritiated water vapor or due to immersed in a cloud of airborne tritium oxide (HTO). Any way of intake of tritium oxide distributes it uniformly through all biological fluids within few hours.  Some other properties of tritium oxide are listed below.

 Properties of tritium oxide 
 Chemical formula  $T_{2}O$ or $^{3}H_{2}O$
 Molar mass  22.0315 g mol−1 
 Density  1.215g/cc
 Melting point  4.49 °C (40.08 °F; 277.64 K) 
 Also called as
 Super-heavy water
 Tritium oxide
 Ditritium oxide

Tritiated Water

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Tritium oxide is also called as tritiated water which can exist in concentrated and dilute forms. The dilute form of tritiated water contains water $(H_{2}O)$ with some HTO $(^{3}HOH)$. Tritiated water is an important part of life science research as it is used to trace the water transport. It is also used to determine the age of various liquids like vintage wines and for the measurement of total volume of water in human body. The process of distribution of tritiated water in our body is very quick and concentration of tritiated water in urine can be same as in the body. The amount of tritiated water can be calculated with the help of given formula.
  • Amount of tritiated water (mg) = Concentration of tritiated water (mg/ml) / Volume of body water (ml)
  • Volume of body water (ml) = [Amount of tritiated water (mg) - Amount excreted (mg)] / Concentration of tritiated water (mg/ml)
Tritiated water is not dangerous externally as beta particles from tritium are unable to penetrate the skin. But the inhalation or ingestion of radiations through food or water can be harmful. The biological half-life of diluted tritiated water is 7 to 14 days. 
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