Hydrogen | Properties, Uses & Facts


Hydrogen is the most abundant element in the universe (70%) and the third most abundant element on the surface of the globe. The lightest element in the universe and the first element in the periodic table, hydrogen have only one proton and one electron. Hydrogen does not have any neutron. It also makes up one of the molecules vital for life: water.

It exists in H+ (Hydronium) and H (Hydride) states. In case of H+ and H bond order is half (1/2).  It has the maximum value of specific heat. Sun’s atmosphere comprises 90% hydrogen. H2 is dried by P2O5 but concentrated sulphuric acid cannot be  used as H2 catches fire in its presence.

In general, hydrogen is rarely found in its pure state, moreover on earth. It is generally combined with other atoms such as Oxygen in water H2O or carbon in hydrocarbons (CH4, C2H6).

It can be found in the gaseous form when two hydrogen atoms are joined together – this is called “Dihydrogen” – and in liquid form when the gas has been cooled to -252.87 °C.

Although hydrogen is the simplest chemical element – it consists of only one proton and one electron – it is one of the most important for life. Luckily, it is the most abundant element in the universe, so for now we don’t have to worry about running out of it. Would you like to know more about what hydrogen is in chemistry? In this article, we answer all of the most common questions about this element.

General properties

  • Symbol: H
  • Atomic number: 1
  • Electrons per energy level: 1
  • Atomic mass: 1.008 u
  • Most stable isotopes: 1 H stable with 0 neutron (99.985%), 2 H (deuterium) stable with 1 neutron (0.015%)
  • Series: non-metals
  • Group, period, block: 1, 1, s
  • Density: 0.00009, 0.07 ( liquid and solid )
  • Point of fusion : -259.14 ° C (dihydrogen)
  • Boiling point: -252.8 ° C (dihydrogen)

History of Hydrogen

In 1671 Robert Boyle described the reaction between iron and dilute acids, which produced hydrogen. The substance will be called ” flammable air ” by Cavendish in 1766, who is also credited with the discovery of hydrogen as an element. Lavoisier fixed the name “hydrogen” in 1783, from “hydro”, “water”, and ” gene “, “to generate”.

Physical Properties

Here are some Physical properties of Hydrogen are given:

  • Hydrogen, made up of H2 molecules, is a colorless and odorless gas.
  • It is the lightest of all bodies.
  • Melting point: -259.2 the C;
  • Boiling point: -252.9 o C;
  • At room temperature it is a gas;
  • Because it is gas, it cannot be seen;
  • Can become a monovalent cation;
  • It can become a monovalent anion;
  • It has no odor (odorless).
  • Its molecules are non-polar; Their molecules interact through induced dipole forces.
  • Its density relative to air is 0.07.
  • It crosses, faster than any other gas, porous walls, and even some red metals.
  • It is the most difficult gas to liquefy after helium.
  • Ordinary hydrogen is a mixture of two isomers, orthohydrogen and parahydrogen, whose molecules have different structures.
  • The hydrogen atom sometimes ionizes in the H form (in discharge tubes), but especially in the H+ form, that is to say in the form of a proton.
  • It cannot exist alone in a polarizable substance: it becomes H3O+ in water.

Chemical Properties

Here are some chemical properties of Hydrogen are given:

  • Not very active when cold, hydrogen gives off numerous reactions when hot or in contact with catalysts.
  • Univalent element, it presents a distinctly electropositive character.
  • It combines directly with most non-metals as well as alkali and alkaline earth metals.
  • The halogens give with it hydracids.
  • It burns with a blue flame, and its mixture with oxygen, detonating on contact with a spark or platinum foam, is employed in the oxyhydrogen torch.
  • Hydrogen combines with hot sulfur and pressurized nitrogen (preparation of ammonia).
  • Particularly greedy for oxygen and chlorine, it can reduce many of their combinations.
  • It reduces oxides of sulfur, nitrogen, arsenic, etc.
  • It also reduces carbon monoxide when hot, giving methane (in the presence of nickel), saturated carbides (Fischer-Tropsch synthesis), or methanol (in the presence of ZnO).
  • The conditions for reduction are improved when the body to be reduced is placed in the same medium where hydrogen is produced (nascent hydrogen, presumably in atomic form).
  • By blowing hydrogen in an electric arc, we obtain Langmuir atomic hydrogen, which reduces all oxides and cold combines with most non-metals.
  • With transition metals, hydrogen gives interstitial compounds, the hydrogen atoms being placed in the voids of the crystal lattice.
  • Certain metals can thus absorb large quantities of hydrogen: certain metal hydrides are the subject of studies for the storage of hydrogen on board vehicles where it would be used as fuel.
  • The most abundant element in the Universe, hydrogen does not occupy the first place on Earth.
  • The atmospheric air contains small quantities of it (3 / 10,000 by volume); in the state of combination, hydrogen appears in the water, in many mineral bodies, and in all organic bodies.
  • It is from hydrogen that the heavier elements are formed in stars, during thermonuclear reactions.

Resemblance of Hydrogen with Alkali Metals

  1. The electronic configuration of hydrogen is same as alkali metals as it has only one electron.
  2. Hydrogen is electropositive in nature like other alkali metals.
  3. It is also good reducing agent like these metals.
  4. By loosing a valance electron, hydrogen also form the cation H+ as M+ is formed by other alkali metals.
  5. Hydrogen shows +1 oxidation state similar to alkali metals.
  6. Like alkali metals, Hydrogen has great affinity for non metals and forms a number of compounds like hydride and oxides.

Resemblance with Halogens

  1. Hydrogen (ns1) needs just one electron to complete its valance shell similar to halogens (ns2,np5).
  2. Like halogens, it is also show non metallic nature.
  3. Hydrogen can show -1 oxidation state by gaining electron and form H, just like halogens.
  4. It can also exist in diatomic state (H2) like halogens.
  5. Its value of ionization is closed to that of halogens.

Preparation of Hydrogen

From Acids

When dilute acids are react with those metals which lies above hydrogen in electrochemical series, hydrogen is produced.

Zn + H2SO4 → ZnSO4 + H2

With dilute HNO3, active metals like Zn, Al, Mg, Fe cannot produce hydrogen.

From Steam


Hydrogen is formed when steam is passed over Fe or Sn.

3Fe + 4H2O Fe3O4 + 4H2

From Alkalis


Hydrogen is formed when metals like Zn, Al, Sn are treated with alkalis like NaOH.

 2Al + 2NaOH + 2H2O → 2NaAlO2 + 3H2

From Hydrocarbons

When alkanes react with water in the presence of catalyst at 1270 K, Hydrogen is formed.

CH4(g) + H2O(g)→ CO(g) + 3H2(g)

C3H8(g) + 3H2O(g) → CO(g) + 3H2(g)

From Natural gas

Hydrogen is formed when natural gas (methane) is mixed with steam and passed over nikel catalyst at 1173 K.

CH4 + H2→ CO + 2H2

By the action of Water on Metals

Hydrogen is formed when cold water is passed over Na, K, and C.

2Na + 2H2O → 2NaOH + H2

When hot water is passed over Mg, Al, and Zn, hydrogen is formed.

Mg + 2H2O Mg(OH)2 + H2

By the action of Water on Ionic Hydrides

CaH2 + 2H2O Ca(OH)2 + 2H2

Water gas shift reaction

CO + H2O → CO2 + H2

Industrial Methods

Bosch and Lane methods are used for the industrial preparation of hydrogen.

1. Bosch Method

In Bosch process, water gas (CO + H2) mixed with steam is passed over the catalyst (Fe3O4 , Cr2O3) and heated up to 450℃ to get hydrogen.

CO + H2 + H2O → 2H2 + CO2

2. Lane Method

In lane method, Iron is passed over super heated steam at high temperature (1000℃) to get hydrogen. Iron can also be generated by passing water gas.

3Fe + 4H2O → Fe3O4 + 4H2

How does Hydrogen produce?

Hydrogen is produced by the separation of chemical elements of which the H atom is a component and by the mobilization of an energy source.

Most hydrogen is currently produced from natural gas and is used by industrialists for its chemical properties, especially in ammonia plants (50% of global consumption) and in oil refineries ( desulphurization of gasoline and diesel, production of methanol, etc. ).

More than 95%  of hydrogen production still comes from fossil fuels (natural gas, petroleum, coal). Hydrogen produced by a renewable or nuclear energy source (or by steam reforming of natural gas if the process is associated with CO2 capture, storage, and recovery unit ) is called “low carbon hydrogen”.

Steam reforming of fossil fuels (or steam reforming)

The most economical reference process (but its cost price remains much higher than that of natural gas). Steam reforming natural gas is the most common method. It breaks the methane (CH4) molecule, the main component of natural gas, which has 4 hydrogen atoms, with water vapor at 900°C. Two successive reactions make it possible to produce hydrogen (H2) and carbon dioxide (CO2) :

CH4 + 2H2O  →    4H2 + CO2

This process generates carbon dioxide which could be captured and stored in the future. Steam reforming of biogas is also possible.

Simple exchange reaction of acids with metals

2Al + 6HCl → 2AlCl3 + 3H2

In the equation above, we can see that when metallic aluminum reacts with hydrochloric acid (HCl), a simple exchange reaction occurs that produces aluminum chloride and hydrogen gas.

Electrolysis of water

A process that requires electricity (profitable if the production of electricity itself presents a low cost). Electric current breaks down the water molecule into hydrogen and oxygen (O2):
H2O + electricity  →    H2 + ½ O2 + heat

This process is the reverse reaction to that occurring in a fuel cell. It makes it possible to produce very “clean” hydrogen (if the electricity is produced using renewable sources) but is not yet economically viable (2 to 3 times more expensive than the steam reforming process). The efficiency of this technique is 40% over the entire line but can reach 80% by recovering the heat.

This electrolysis has different variants, at different temperatures:

  • Low temperature (<200 ° C) alkaline electrolysis using an aqueous solution of sulfuric acid (H2SO4) or potassium hydroxide (KOH);
  • Low-temperature electrolysis (<200 ° C) using a solid electrolyte: PEMFC polymer membrane which conducts protons ( Proton Exchange Membrane Fuel Cell );
  • High-temperature electrolysis (> 400 ° C ) using an oxygen ion conductive ceramic membrane ( Solid Oxide Fuel Cell), which must be coupled to a concentrating solar system at a high-temperature nuclear reactor to take advantage of a source of low-cost steam;
  • Gasification and pyrolysis of biomass (in particular charcoal): a process under research and development which, for example, makes it possible to obtain hydrogen by chemical transformation of wood at very high temperature (between 1,200 ° C and 1,500 ° C). A gas mixture is obtained containing hydrogen (H 2 ) and carbon monoxide (CO). After purification of this mixture, hydrogen is obtained.
  • Other processes at the state of research: other hydrogen production techniques are currently under study such as phot electrolysis (photoelectrochemical cell decomposing water under the effect of light), thermochemical decomposition of water (the water is heated to 800/1000 ° C thanks to nuclear energy) or microorganisms (production of hydrogen by bacteria modified under the effect of sunlight).

Isotopes of Hydrogen

Hydrogen is the only element for which each isotope has a specific name because their difference in mass relative to hydrogen is significant: from single to double or triple, which explains that, unlike what is true for isotopes in In general, these differences can influence the chemical properties of deuterium or tritium relative to protium (isotopic effect). The heavy water (DO) is toxic for example (high dose) for many species because of the large difference in mass between the isotopes of kinetic reactions in aqueous solution “heavy” slowed considerably…

The known isotopes of hydrogen are:   


When combined with ionic compounds, this isotope can acquire a negative or positive charge. It is the most abundant (~ 99.98%). Simply made up of a proton and therefore not having a neutron, it is a stable isotope.


It is a heavy and stable isotope, has only one neutron and one proton in its nucleus, is generally used in nuclear fusion processes. Its name derives from the Greek ” deuteros ” and means “second”.


This is the most frequent and abundant type of isotope. Its core structure is composed of a proton and two neutrons, being highly radioactive. This isotope is widely used in weapons manufacturing environments for testing purposes.

Isotopes of hydrogen
Isotopes of Hydrogen

Hydrogen is a rare element in the Earth’s atmosphere as it has a light density and easily escapes Earth’s gravity. However, it is an element in abundance on the surface in the form of hydrocarbons and water (H2O), there being, comparatively, two hydrogen atoms for each of the oxygen atoms. Through the Bohr atomic model, it was feasible to explain the behavioral mechanisms of hydrogen.

The chemical reactions of Hydrogen

At room temperature, the reactivity of hydrogen is low. It rises significantly when heated.

Reaction with Nitrogen:

When hydrogen is react with nitrogen (3∶1) at 480-500℃ and 200atm pressure in the presence of iron catalyst, produced ammonia.

N2 + 3H2 → 2NH3

Reaction with metals

Hydrogen react with metals at high temperature to form metal hydride.

2Li + H→ 2LiH

Ca + H2 → CaH2

Mg + H2 → MgH2

2Na + H→ 2NaH

Reducing Properties

Hydrogen can reduced metal oxides into metals.

Fe3O4 + 4H2 → 3Fe + 4H2O

Ag2O + H2 → 2Ag + H2O


Hydrogen combines with all elements (except noble gases and with metals of group 7, 8 and, 9) and form binary hydrides. Now we discuss three types of hydrides:

1. Saline or Ionic Hydride

Ionic hydrides are also called salt-like hydrides or electrovalent hydrides. These are formed by the low electronegativity elements like Li, Ca (s-block metals) by the transfer of an electron from these elements to hydrogen atom.

2Li + H2 → 2LiH

Ca + H2 → CaH2

During the formation of such hydrides a part of energy is released which makes hydrogen molecules hyperactive. These hydrides are non-volatile and non conducting crystalline solids.

2. Metallic or Interstitial hydrides

Metallic hydrides are formed by transition or inner transition elements like ScH2, LaH2, VH. These hydrides have metallic in nature and posses almost similar characteristics to the parent metal atom. In solid state, these hydrides are good conductor of electricity and used to store hydrogen in fuel cells. Interstitial hydrides are non-stoichiometric in nature like TiH1.73, ZrH1.92.

3. Covalent or Molecular hydrides

Hydrogen is combine will all p block elements except noble gases and form covalent hydrides like CH4, NH3,HF. These hydrides have general formula MH8-n (where n is the number of valance electron of non metal) for example CH4, NH3, HX. These hydrides are volatile and have low melting and boiling point.

Hydrogen bomb

The hydrogen bomb, H bomb, or thermonuclear bomb is the atomic bomb that has the greatest potential for destruction. Its operation stems from a nuclear fusion process, which is why it can also be called a fusion bomb.

The explosion of a hydrogen bomb results from the fusion process, which takes place at very high temperatures, approximately 10 million degrees Celsius. The production process of this bomb begins with the union of hydrogen isotopes, called protium, deuterium, and tritium. The junction of hydrogen isotopes makes the nucleus of the atom generate even more energy because helium nuclei are formed, whose atomic mass is 4 times greater than that of hydrogen.

Thus, the core that was light becomes heavy. Therefore, the nuclear fusion process is thousands of times more violent than the fission one. The strength of a hydrogen bomb can reach 10 million tons of dynamite, releasing radioactive material and electromagnetic radiation at a level far superior to that of atomic bombs.

The first test of a hydrogen bomb, in 1952, released an amount of energy equivalent to about 10 million tons of TNT. It is noteworthy that this type of reaction is the energy source of stars like the Sun. It is composed of 73% hydrogen, 26% helium, and 1% other elements. This is explained by the fact that fusion reactions take place in its nucleus, in which hydrogen atoms fuse to form helium atoms.

Fun Facts About Hydrogen

  • The hydrogen Molecular is lighter than air and was used in the rigid airships German count Ferdinand von Zeppelin, hence the name of the airship;
  • The molecular form can be synthesized by some bacteria and algae;
  • The hydrogen can be used in the production of clean energy fuel;
  • Methane gas (CH4) is an increasingly important source of hydrogen.

Green hydrogen: a fuel full of potential to save the climate

In the sense of sustainability and preservation of the environment, “green hydrogen” is a term used to refer to hydrogen obtained from renewable sources, in a process in which there is no carbon emission. Unlike fossil fuels, the energy use of hydrogen rarely takes place through its combustion, but rather through an electrochemical transformation, carried out in cells known as fuel cells.

In this equipment, the oxygen existing in the atmosphere combines with hydrogen, producing electricity and water. In other words, the energy generation process using fuel cells itself does not impact the environment, which is why it can be classified as a clean process.

Uses of Hydrogen

  1. Hydrogen is used in oxy-hydrogen flame: When a mixture of hydrogen and oxygen is burnt, very high temperature of about 2500℃ is produced. The flames with such a high temperature can cut or weld metals because metals have high melting points. So, oxy-hydrogen flames are used for cutting or welding of metals.
  2. Hydrogen is used for the synthesis of compounds: For example large quantities of hydrogen is used in the manufacturing of ammonia by Haber process. This ammonia is further used in the manufacture of fertilizers, explosives and as a refrigerant.
  3. Hydrogen also act as a strong reducing agent: For example hydrogen reduces metal oxides to respective metals at high temperature. When hydrogen is passed over lead oxide, then lead oxide is reduces to lead. Similarly, when hydrogen is passed over cupper oxide then cupper oxide reduces cupper
  4. As hydrogen is the lightest gas, it is also used in meteorological balloons: A meteorological balloon is a balloon that carries instruments up in the air to sent back information on atmospheric pressure, temperature, humidity and wind speed. Hydrogen mixed with helium is used for filling of meteorological balloons and airships.
  5. Hydrogen is also used for hydrogenation of oils: When hydrogen gas is passed through vegetable oils in the presence of finely divided nikel which acts as catalyst at a temperature of about 300℃ to form vegetable ghee. This process is known as hydrogenation of oils. It increases the life of oils.
  6. Hydrogen is used in the formation of synthetic petrol: When coal in the form of coal gas is hydrogenated in the presence of catalyst such as iron at high temperature (150 to 300℃) and pressure (5 to 10atm), it produces a liquid mixture of compound similar to petrol. This liquid mixture is known as synthetic petrol.
  7. Hydrogen is also used as a fuel: Hydrogen has a very high heat of combustion, therefore it is used as fuel in the form of coal gas, water gas and liquid hydrogen. A mixture of liquid hydrogen and liquid oxygen is used as rocket fuel.

In future, hydrogen gas could replace gasoline in auto mobiles or can be used with oxygen gas in fuel cells to generate electricity. Hydrogen can also called clean fuel because when hydrogen undergoes combustion, it produces only water. Therefore, it is non-polluting fuel.

Advantages of using Hydrogen as an Automobile fuel

The use of liquid hydrogen as an automobile fuel has the following advantages:

  1. The amount of energy per unit mass of the fuel is very high.
  2. The emission of CO, CO2, oxides of Sulphur, nitrogen, aldehydes etc. is reduced by the combustion of hydrogen. Hence, the use of hydrogen is more safe and does not cause any pollution.
  3. The technology needed to modify internal combustion energies for the use of hydrogen as a fuel is simple and does not involve mush cost.
  4. The fuel cells involving the catalytic combustion of hydrogen are already being used in successfully and have an efficiency of about 70 to 80%.

1. Hydrogen is:

a) Electropositive

b) Electronegative

c) Both electropositive as well as electronegative

d) Neither electropositive nor electronegative

2. Dihydrogen has:

a) Two isotopes and no isomers

b) Three isotopes and two nuclear isomers

c) Three isotopes and two optical isomers

d) Two isotopes and two geometrical isomers

3. Reaction between following pairs will produce hydrogen except:

a) Cu + HCl

b) Fe + H2O(g)

c) Mg + H2O (hot)

d) Na + Alcohol

4. The oxidation states exhibited by hydrogen in its various compounds are:

a) -1 only

b) Zero only

c) +1, -1 and zero

d) +1 only

5. Which of the following groups represents the saline hydrides:

a) NaH, KaH, CaH2

b) NaH, SiH4, CaH2

c) NH3, BH3, AlH3

d) None of these

6. Temporary hardness of water is due to the presence of:

a) MgSO4

b) Ca(HCO3)2

c) CaCl2

d) CaCO3

7. Permanent hardness of water is due to the presence of:

a) CaSO4

b) MgSO4

c) Ca(HCO3)2

d) NaHCO3

8. Water can be tested by:

a) Smell

b) Taste

c) Hydrated CuSO4

d) Anhydrous CuSO4(white) which changes to blue

9. Bleaching action of H2O2 is due to its:

a) Oxidizing nature

b) Reducing nature

c) Acidic nature

d) Thermal instability

10. What would happen when a small quantity of H2O2 is added to a solution of FeSO4:

a) Colour of FeSO4 disappears

b) H2 is evolved

c) An electron is added to Fe2+

d) An electron is lost by Fe2+

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