Occurrence, Position and Isotopes of Hydrogen

Introduction:

Hydrogen, the most abundant element in the universe and the third most abundant on the surface of the globe. Hydrogen has the simplest atomic structure among all the elements around us in Nature. In atomic form it consists of only one proton and one electron. However, in elemental form it exists as a diatomic (H₂) molecule and is called dihydrogen.

Occurrence:

Dihydrogen is the most abundant element in the universe (70% of the total mass of the universe) and is the principal element in the solar atmosphere. The giant planets Jupiter and Saturn consist mostly of hydrogen. However, due to its light nature it is much less abundant (0.15% by mass) in atmosphere. In the combined form it constitutes 15.4% of the earth's crust and the oceans. In the combined form besides in water, it occurs in plant and animal tissues, carbohydrates, proteins, hydrides including hydrocarbons and many other compounds.

· It is the third most abundant element on the surface of the globe.

· On the earth it is the ninth element in abundance.

Position of Hydrogen:

Hydrogen is the first element in the periodic table. The elements in the periodic table are arranged according to their electronic configurations. Hydrogen has electronic configuration 1s¹. On one hand, its electronic configuration is similar to the outer electronic configuration (ns¹) of alkali metals, which belong to the first group of the periodic table. On the other hand, like halogens (with ns² np⁵ configuration belonging to the seventeenth group of the periodic table), it is short by one electron to the corresponding noble gas configuration, helium (1s²).

Position of Hydrogen in Periodic Table:

Hydrogen, therefore has resemblance to alkali metals which lose one electron to form unipositive ions as well as with halogens, which gain one electron to form uninegative ion. Like alkali metals, hydrogen forms oxides, halides and sulphides. In fact, in terms of ionization enthalpy, hydrogen resembles more with halogens. Like halogens, it forms a diatomic molecule.

In terms of reactivity, it is very low as compared to halogens. This is extremely small as compared to normal atomic and ionic sizes of 50 to 200pm. As a consequence H⁺ does not exist freely and is always associated with other atoms or molecules. Thus, it is unique in behaviour and is therefore best placed separately in the periodic table. It is placed on the left side on the periodic table.

Isotopes of Hydrogen:

Isotopes are the different atoms of the same element which have the same atomic number but diferent mass number.

Occurrence of Isotopes:

· The most abundant isotope of hydrogen is protium.This in natural hydrogen to an extent of 99.4844%.

· The remaining 0.0156% being deuterium.

· Tritium being unstable because of its radioactive nature.

· The natural abundance of , are in the ratio of 1 : 1.56 × 10^-2 : 1 × 10^-18.

Hydrogen has Three Isotopes:

· Protium ()

· Deuterium or D ()

· Tritium or T ()

These isotopes differ from one another in respect of the presence of neutrons.

Ordinary hydrogen, protium, has no neutrons, deuterium (also known as heavy hydrogen) has one and tritium has two neutrons in the nucleus. Hydrogen without any neutron is protium. Hydrogen with one neutron is deuterium. Hydrogen with two neutrons is tritium.

1. Protium or Ordinary Hydrogen ():

· Protium, in physics and chemistry means hydrogen-1 the most common isotope of the element hydrogen.

· Its atomic number =mass number=1 and its exact mass is 1.007825 amu.

· It is a nonradioactive element.

· It has only one electron, one proton and zero neutron.

2. Deutrium or Heavy Hydrogen ( or D):

· Deuterium is a hydrogen isotope consisting of one proton, one neutron and one electron.

· Deuterium is roughly twice the mass of protium (deuterium has a mass of 2.014102 amu).

· It is a radioactive element.

· Chemically, deuterium behaves similarly to ordinary hydrogen (protium), but there are differences in bond energy and length.

Deutrium

3. Tritium ( or T):

· Its nucleus, consisting of one proton, one electron and two neutrons, has triple the mass of the nucleus of ordinary hydrogen. 

· Tritium is a beta-emitting radioactive isotope of hydrogen.

· It has an atomic mass of 3.0160492 u.

· It has an atomic mass of 14.

Protium	Deutrium	Tritium
1 proton, 1 electron, 0 neutron.	1 proton, 1electron, 1 neutron.	1 electron, 1proton, 2 neutron.
Non-radioactive element.	Radioactive element.	Radioactive element.
Common isotope of hydrogen.	Stable isotope of hydrogen.	Radioactive isotope of hydrogen.