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Molecule of Hydrogen – Properties, Methods of Preparation.

Nov 8, 2022

Molecule of Hydrogen  




molecule of hydrogen



Molecular hydrogen, also known as dihydrogen, is a diatomic molecule made up of two hydrogen atoms joined by a covalent bond with the chemical formula H2. The molecule of hydrogen is used in the hydrogenation of fats and oils, and it is also occasionally used to fill balloons. molecules of hydrogen can adsorb not only on metal surfaces, but also on carbon, zeolites, alumina, and silica surfaces.

One of the most abundant atoms or elements present in the universe is hydrogen. It constitutes about 90 per cent of all the atoms in the universe. Its atomic number is one, and with an atomic weight of 1.008, it is the lightest and smallest of all the elements in the periodic table. The molecule of hydrogen is generally found in a gaseous state. It mostly exists as an odourless and colourless gas that is highly flammable.


As the atomic number of hydrogen is one, it is the first element in the periodic table. It has some features that are identical to halogens and alkali metals. However, recently, in some studies, scientists have discovered that hydrogen is also present in its metallic form. Like other alkalis, its outermost shell contains one electron, and its ionization energy is similar to that of halogen atoms. 

Even though hydrogen is available in a large quantity in nature, it is rarely found in nature in a free state. Most of the time, it can be found bonded to other elements in chemical compounds. For example, in a water (H2O) molecule, the H2 molecule is bonded to an oxygen atom. It is interesting to know that when we burn hydrogen, it reacts with oxygen in the air and forms water. In fact, this phenomenon has given a molecule of hydrogen its name. The name is derived from the Greek word “hydro genes”, which means creator of water.


Occurrence of Molecule of Hydrogen 

As mentioned earlier, the H2 molecule is the most abundantly found element in the universe and constitutes 70% of the mass of the whole universe. In its molecular form, it is found as dihydrogen. Hydrogen is also the main element in the solar system, with the biggest planets, Saturn and Jupiter, mainly made up of hydrogen. In its combined state, hydrogen forms 15.3 per cent of the crust of the Earth and the oceans.

Discovery of Molecule of Hydrogen 

A British scientist named Henry Cavendish first discovered a molecule of hydrogen in the year 1765, and he named it “inflammable air.” The French scientist Antoine Lavoisier coined the name “hydrogen” in 1783.


Isotopes of Hydrogen 

Hydrogen has mainly three isotopes, all of which have the same electronic configuration. Therefore, their chemical properties are also identical. However, as their mass numbers are different, the physical properties of the isotopes of hydrogen are quite different. Below are the three isotopes of hydrogen:

Isotopes Atomic Mass Atomic Number Number of Protons Number of Neutrons
Deuterium 2 1 1 1
Protium 1 1 1 0
Tritium 3 1 1 2

Out of the three isotopes of a molecule of hydrogen in the table above, protium is the commonest one and is found in abundance in nature.


Position of Hydrogen in Periodic Table

Hydrogen is identical to alkalis and halogens. That is why it lies at the top of the periodic table.

What is the resemblance of hydrogen with alkalis?

  1. Both hydrogen and alkali metals have a valency of one.


H (Z=1) – K1

Li (Z=3) – K2, L1

Na (Z=11) – K2, L8, M1

K (Z= 19) – K2, L8, M8, N1 

  1. Both the elements of group I A and H2 molecule have the same outer configuration ns1


H (Z=1) – 1s1

Li (Z=3) – 1s2, 2s1

Na (Z=11) – 1s2, 2s2, 2p6, 3s1

K (Z= 19) – 1s2, 2s2, 2p6, 3s2, 3p6, 4s1

  1. Just like alkali metals, hydrogen also gives rise to halides. 


I-A: NaCl, KBr.

Hydrogen: HCl, HI.

  1. The hydrogen gas is released at the cathode during electrolysis. 
  1. Both hydrogen and alkali metals have an oxidation state of +1.
  1. Just like the halides of alkali metals, hydrogen halides undergo ionization in an aqueous medium. 


HCl(aq)→ H+(aq) + Cl–(aq)

NaCl(aq)→ Na+(aq) + Cl–(aq)

  1. Non-metal compounds like alkali metals may also be formed by hydrogen.


Hydrogen: H2S

I-A: Na2S

How does hydrogen resemble halogens?

  1. Halogen, as well as hydrogen, are non-metals, with the exception of iodine which is partially metallic.
  2. The electronegativity of hydrogen is higher (2.1).
  3. Both of them have a high ionization potential. 
  4. Hydrogen easily accepts one electron to form a hydride ion (H–), the same way halogen accepts one electron to form a halide ion (X–).
  5. Compounds with non-metals are formed by both hydrogen and halogen.


Halogen: HCl (H is non-metal)

Hydrogen: H2S (S is non-metal)

Therefore, the resemblance of hydrogen is more with halogen than it is with alkali metals. That is why its position in the periodic table is not justified.

Differences in Hydrogen From Halogens and Alkali Metals:

  1. The electropositivity of hydrogen is lesser than alkali metals, and its electronegativity lesser than halogens.
  2. Hydrogen has only one proton in its nucleus. It also has an electron outside the nucleus, but there are no neutrons.
  3. The sizes of the ions of alkali metals are much bigger than those of hydrogen ions.
  4. The K+ and Na+ ions are stable in the water, while hydrogen ions (H+) are unstable.

Properties Of Hydrogen

Physical Properties Of Hydrogen

  • Hydrogen is an odourless, colourless, and neutral gas
  • Hydrogen is less soluble in water
  • It is highly inflammable and burns with a blue flame
  • Its boiling point is very low

Chemical Properties Of Hydrogen

  • At room temperature, dihydrogen is fairly inert because H–H bond has a relatively strong bond enthalpy.
  • A high electric arc is needed to produce atomic hydrogen as its orbit is not complete with one electron.
  • Hydrogen is capable of combining with almost every element.

Different Forms of Hydrogen

Atomic Hydrogen:

Atomic hydrogen is created when we pass molecular hydrogen through an electric arc. There are two tungsten electrodes around this electric arc, and its temperature is 2273K The heat produced during this process is stored in the atoms.

H2→ 2H- Heat 

The hydrogen atoms released in the reaction again combine and form H. A large amount of energy is liberated in the process, which is used for welding purposes.

Nascent Hydrogen:

When the hydrogen is generated or just liberated, it is called nascent hydrogen. It is a more powerful reducing agent than normal hydrogen and is much more reactive.

Methods of Preparation of Molecule of Hydrogen

  1.  By the electrolysis of water:


2. The reaction of actions with strongly electropositive metals

2Na+ + H2SO4 —→ Na2SO4 + H2 (2 molecules of hydrogen)

2K+2HCl→ 2KCl+ H2 ( 2 molecules of hydrogen)

         3. The reaction of water with strongly electropositive metals: 

2Na + 2H2O —→ 2NaOH + H2 (2 molecules of hydrogen)

          4. The reaction of alkali with metals like Zn and Al

6NaOH (Hot & Concentrated) + 2Al —→ 2 Na3Alo3 + 3H2

Zn + 2NaOH —→ Na2 + ZnO2 + H2 (2 molecules of hydrogen)

           5. The reaction of hydrogen with oxygen 

When hydrogen reacts with dioxygen, water is formed. 

H2 + 12O2 →[Δ] 200 ∘ CH2O Nascent hydrogen

              6. The reaction of hydrogen with metals

Hydrogen reacts with many metals at high temperatures to produce the corresponding hydride. For example, 

2Na + H2 (2 molecules of hydrogen) →[Δ] 350 ∘ C2NaH ( Sodium hydride)

               7. The reaction of hydrogen with halogens

Hydrogen reacts with halogens to form hydrogen halides.

H2 + F2 → dark 2HF

H2 + Cl2 → sunlight 2HCl

H2 + Br2 → 350 ∘ C2HBr

H2 + I2 → 2HI

            8. Reactions of hydrogen with organic compounds:

Hydrogen reacts with many organic compounds to produce commercially important products in the presence of certain catalysts. For instance,

  • In the presence of a nickel catalyst, vegetable oils are hydrogenated.
  • When hydroformylation of olefins occurs, aldehydes are formed, which then give alcohol.

Uses of Hydrogen

Below are some of the uses of hydrogen:

  • It is used to prepare ammonia.
  • It is used in the preparation of fuel gases like water gas.
  • Hydrogen is employed as a reducing agent in metallurgy.
  • In the nuclear fusion reaction of hydrogen, a huge amount of energy is liberated in stars.


Hydrogen is one of the most important elements in the periodic table, and its reactions are of great importance in nature as well as for commercial use. Therefore, having knowledge of it is important. We hope this blog helped you gain the required knowledge on the topic.

Frequently Asked Questions

Q) Why is nascent hydrogen more reactive than ordinary hydrogen?

A) A nascent hydrogen gas molecule is more reactive than ordinary hydrogen because it is in an atomic state, and atoms are more reactive than molecules. Also, their internal pressure is higher.

Q) What are the allotropes of hydrogen?

A) Following are the two isomeric forms in which molecular hydrogen occurs:

  1. Ortho-Hydrogen: In this allotrope of hydrogen, there is a parallel alignment of two proton nuclear spins.
  2. Para-Hydrogen: In this allotrope of hydrogen, there is an antiparallel alignment of two proton nuclear spins.

Q) Do hydrogen gas molecules burn in the air?

A) Yes, hydrogen gas molecules react with oxygen in the air to give H2O or water. Some amount of energy is also released in the process. 

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