Isotopes of Hydrogen

 

Isotopes of Hydrogen

Definition

The existence of isotopes of elements was first discovered by J.J. Thomson in 1913. The name of isotope was introduced (assigned) by Soddy because they have the same atomic number and hence occupied the same place in the periodic table. (Isotope is a Greek word; iso = same; topos = place). Nearly all elements found in nature are mixture of several isotopes.[There are 287 different isotopic species in nature].

“Isotopes are atoms of the same element having same atomic number but different mass numbers (atomic masses). In other words isotopes are different forms of atoms of an element which have same number of protons (and also electrons) but different number of neutrons in their respective nuclei”.

Different isotopes of an element have same chemical properties due to their identical electronic configuration (i.e. same number of electrons in the shells) but they have different physical properties because of their different atomic masses.

Same properties of isotopes	Different properties of isotopes
1. Atomic number	1. Mass number
2. Electronic configuration	2. Atomic mass
3. Number of electrons	3. Number of neutrons
4. Number of protons	4. Nuclear mass
5. Chemical properties	5. Physical properties
6. Same position in periodic table

Out of 92 natural elements, 23 elements have no isotopes, each consisting of only one kind of atoms. [It is strictly improper to refer to elements that exist in only one atomic form as having “one isotope”; actually such elements as Be, F, Na, Al, P, Sc, Mn, Co, As, Y, Nb, Rh, Cs, Pr, Tb, Ho, Tm, Bi etc have no isotopes i.e. they have no other atomic form that is like them in all respects except mass. The term isotope requires the existence of at least two elemental forms, in the same sense that the word twin requires the existence of a pair. Recently the term monoisotopic is evolved for elements found in nature as a single atomic or isotopic form]. The remaining 69 natural elements have 2 to 10 isotopes each.

The heavier isotopes of elements usually occur very rarely in the atomic population (e.g. 1 part in 4500 for ²H, 1 part in 140 for U-235; in the exceptional case of chorine, the ratio of isotopes 35 and 37 is about 3 to 1).

Isotopic Forms of Hydrogen
Hydrogen exists in three isotopic forms
1. Protium.
2. Deuterium.
3. Tritium.

Summary of Characteristics of Isotopes of Hydrogen

 

Protium

1. It is the simplest isotope and it is just ordinary hydrogen.

2. It is symbolized as ₁H¹ having one proton in the nucleus and one electron in 1s orbital and no neutron. It is the only isotope of hydrogen having more proton than neutron.

3.It is the most abundant isotope of hydrogen with an abundance of 99.88% [i.e. naturally free occurring  hydrogen contains about 99.88% Protium].

Deuterium

     1. It is the natural heaviest isotope of hydrogen and hence also known as Heavy Hydrogen.

2.  It is represented as ₁H² having one neutron in the nucleus in addition to one proton and one electron in    K-shell. It is the only isotope of hydrogen having same number proton, neutron and electron.

3.  It has an abundance of 0.0156% of terrestrial hydrogen (in the ratio of one atom of deuterium to 6000  atoms of ordinary hydrogen i.e. 1:6000 (1:1500 in book).

4.    It is used as a moderator in fission power rectors to slow down neutrons.

Tritium  

   1.   It is the artificial radioactive isotope of hydrogen with half life of 12.5 years.

2.  It is symbolized as ₁H³ having two neutrons in addition to one proton in the nucleus and one electron in K-shell. It is the only isotope of hydrogen having more neutron than proton.

3.   It has a very minute abundance of 4 x 10^–15% (4 x 10^–50% in some books) [in the ratio of one atom of tritium to every 10¹⁸ atoms of ordinary hydrogen i.e. 1: 10¹⁸ (1:10⁷ in some books)].

4.It is formed in the environment by cosmic ray bombardment.

5. It is used in thermonuclear weapons, fusion reactions, in making hydrogen or fusion bomb, in making  luminous paints and as a tracer.

 

Heavy Water/Dueteride

Deuterium reacts with oxygen to form Deuterium Oxide (D₂O) which is commonly called Heavy Water due to being 1.1 times heavier than ordinary water. Heavy water or deuterium oxide or dueteride is a binary compound of deuterium or heavy hydrogen with oxygen formulated as .It is used as a moderator.

 

Difference between Heavy and Ordinary Water