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Allotropes: H2  
Group: 1 
Group name: (none)  
Period: 1   
Block: s 
Electron configuration: 1s1
Shell structure: 1  
Atomic number: 1   
State at 20°C: Gas   
Electrons: 1
Protons:   1
Melting point: −259.16°C, −434.49°F, 13.99 K
Boiling point: −252.879°C, −423.182°F, 20.271 K
Density (g cm−3) :    - 0.000082
Relative atomic mass: 1.008  
Key isotopes: 1H, 2H
CAS number: 133-74-01333-74-0 (H2)

Definition of Hydrogen

A hydrogen is a Group 1 and the first element in the Periodic Table with the symbol name H and having atomic number 1.  It has no color, odor, or taste and it is a non-toxic gas. It is the lightest gas in the atmosphere which means it is lightest even than the air. Among all the elements, hydrogen has the simplest structure comprising one proton and an electron.

It is a highly combustible gas which means it can easily burn in the air the flame being invisible and with the enthalpy of combustion of −286 kJ/mol. A hydrogen atom’s electron has a ground state energy level of about 13.6 eV and the energy levels can be measured easily using the Bohr model of the atom

History of Hydrogen

  • In the early 1500s, the alchemist Paracelsus noted that the bubbles given off when iron filings were added to sulfuric acid were flammable. In 1671 Robert Boyle made the same observation during a reaction between iron fillings and dilute acids, that resulted in the production of hydrogen gas but neither of them followed up their discovery of hydrogen.
  • Finally, Hydrogen was discovered in 1766 by English scientist Henry Cavendish by reacting acids on metals. He prepared it by reacting hydrochloric acid with zinc. In 1781, he was the first to establish the fact that it produces water when burned.  When the French Chemists Antoine Lavoisier and Laplace replicated this fact, they gave the element the name hydrogen (from the Greek – hydro meaning “water” and genes meaning “former”).
  • He described hydrogen as “inflammable air from metals” and established that it was the same material (by its reactions and its density) regardless of which metal and which acid he used to produce it. 
  • Cavendish also observed that when the substance was burned, it produced water thereby dismissing the belief that water was an element.
  • Later in 1898, the British Chemist and physicist James Dewar presented the liquefied version of the gas by using regenerative cooling and a vacuum flask. The following year, solid hydrogen was also introduced by him. 

Features of Hydrogen

  • It is a colorless, odorless, and non-toxic gas with the formula H2. It has the lowest density of all gases. 
  • It is a nonmetallic element and It can become metallic at very high pressures. It forms a single covalent bond with most nonmetallic elements and forms compounds like water (H2O), and hydrocarbons (consisting entirely of hydrogen and carbon). In fact, hydrogen is the only element that forms the maximum number of compounds. 
  • With stronger electronegative elements like halogens (F, Cl, Br, I), or oxygen, hydrogen can form compounds. In these compounds, hydrogen acquires a partial positive charge. Hydrogen can also take on a partial negative charge in combinations containing less electronegative elements like metals and metalloids. These compounds are commonly referred to as hydrides.

Isotopes of Hydrogen

  • There are mainly three naturally occurring isotopes of hydrogen namely protium, deuterium (D), and tritium (T). The elements having the same atomic number but a different mass number are called isotopes. Protium (1H) is the most common with an abundance of more than 99.8%. It is a stable isotope because the proton never decays. Deuterium (2H) is used neutron moderator and coolant for nuclear reactors. Tritium (3H) is the only radioactive isotope and decays into helium-3 through beta decay. It is used in nuclear weapons, controlled nuclear fusion, luminous paint, self-powered lighting, and many other purposes. The other isotopes (4H to 7H) are not naturally occurring but are made in the laboratory.


  • Hydrogen is present in all organic compounds and makes up about 70% of the universe by weight. Hydrogen is easily the most abundant element in the universe. It is found in the sun (About three-quarters of the sun is hydrogen), and most of the stars, and the planet Jupiter is composed mostly of hydrogen. It is present on the Earth’s surface in very small amounts because it easily escapes the Earth’s atmosphere to outer space. It is very scarce as a gas – less than one part per million by volume. But it is abundantly available in the form of molecules like water and organic compounds and it is an element that is present in all beings like humans, animals, plants, fruits, etc.  Around 10 percent of the mass of the human body is hydrogen. Also, the only free hydrogen on earth can be found deep underground.

Hydrogen: The Fuel of the Future

Hydrogen, the most abundant element in the universe is a clean alternative to methane, also known as natural gas. It has the capability to change our dependency on fossil fuels. Hydrogen gas on burning (combustion) with oxygen (air) generates a considerable amount of energy, generally, 2,86,000 joules per mole of Hydrogen gas burned. Hydrogen is a clean fuel that can be produced from diverse domestic resources like natural gas, nuclear power, biomass, and renewable power like solar and wind with the potential for near-zero greenhouse gas emissions. On production it generates electrical power in a fuel cell, emitting only water vapor and warm air. Today, hydrogen fuel can be produced by different methods like natural gas reforming, electrolysis (a process of separating water and oxygen), solar-driven and biological processes. Hydrogen fuel can be used in cars, in houses, for portable power, and for many other uses. The best thing is that it is clean and environment-friendly.

Methods of preparing

Hydrogen can be produced through several methods, including:

  • Steam Methane Reforming (SMR): A reaction between methane (natural gas) and steam to produce carbon dioxide and hydrogen.
  • Electrolysis: An electrical current is passed through water to separate the hydrogen and oxygen molecules.
  • Biomass Gasification: The conversion of organic matter into hydrogen through a high-temperature process.
  • Coal Gasification: The conversion of coal into hydrogen through a high-temperature process.
  • Photoelectrochemical Water Splitting: The use of light to split water into hydrogen and oxygen.
  • Thermolysis: The thermal decomposition of organic compounds to produce hydrogen.

Each method has its advantages and disadvantages, and the choice of method depends on factors such as cost, efficiency, and the availability of resources.

Uses of Hydrogen

  • Hydrogen has many uses. In the chemical industry, it is used to make ammonia for agricultural fertilizer (the Haber process) and cyclohexane and methanol, which are intermediates in the production of plastics and pharmaceuticals. It is also used to remove sulfur from fuels during the oil-refining process. Large quantities of hydrogen are used to hydrogenate oils to form fats, for example, to make margarine.
  • Hydrogen gas was used in lighter-than-air balloons for transport but was very unsafe because of the fire risk involved (Hindenburg). Hydrogen is highly flammable and has an almost invisible flame, which can lead to accidental burns.
  • It burns in the air to form only water as a waste product and if hydrogen could be made on a sufficient scale other than fossil fuels then there might be a possibility of a hydrogen economy. 
  • Liquid hydrogen is used as a rocket fuel, for instance, using it in the space shuttle’s lift-off and ascent into orbit. 
  • Hydrogen is seen as a clean fuel because it is generated from water and returns to water when oxidized. This is why hydrogen-powered fuel cells are being seen as environment-friendly sources of energy and also is used in some vehicles.
  • Hydrogen is being used as a protective atmosphere for making flat glass sheets.
  • Hydrogen was used in many of NASA’s rockets, including the second and third stages of the Apollo Program’s Saturn V and the Space Shuttle main engines, are powered by burning liquid hydrogen with pure oxygen.
  • Hydrogen was used in creating Zeppelin, the first trusted mode of air travel invented by German count Ferdinand von Zeppelin. By the year 1914, more than 35,000 passengers became part of the air journey and during World War 1, hydrogen-lifted airships were deployed as bombers and observation platforms. But, it was banned as a source of airships after the explosion of the zeppelin Hindenburg. Hydrogen is still used, in preference to non-flammable but more expensive helium, as a lifting gas for weather balloons. 


Hydrogen is an essential part of life and the universe. Without hydrogen, even the Sun would not have existed. And that the most essential substance for life’s existence, water, would not exist. It is such a useful substance that now it is being planned to introduce hydrogen as a fuel to eliminate the dependency on fossil fuels. At the same time, it is extremely combustible. In other words, it has a tendency to burst into flames. This tendency makes hydrogen both a very dangerous and a very useful resource depending on the usage. For example, the engines of space shuttles are powered by none other than burning liquid hydrogen and liquid oxygen. So, if used with care and caution, it can be more useful than harmful.  


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