Symbol H
Atomic Number 1
Atomic Mass 1.008
Discovered by Hydrogen was discovered by Henry Cavendish

Physical Properties of Hydrogen

Group 1 Melting point −259.16°C, −434.49°F, 13.99 K
Period 1 Boiling point −252.879°C, −423.182°F, 20.271 K
Block s Density (g cm−3) 0.000082
Atomic number 1 Relative atomic mass 1.008
State at 20°C Gas Key isotopes 1H, 2H
Electron configuration 1s1 CAS number 133-74-0
ChemSpider ID 4515072 ChemSpider is a free chemical structure database

What is Hydrogen?

  • To start the tour with the periodic table of elements, the first element to come across is Hydrogen, whose chemical symbol is H. It is the first and most basic among all the elements in the universe. It is also the lightest element in the periodic table, and 90% of all the atoms in the universe are hydrogen atoms.
  • The chemist Lavoisier gives the name hydrogen. It got its name from the Greek word “hydro” meaning water. Lavoisier knew that it existed in every water molecule.

Preparation of Dihydrogen – H2

1. Laboratory Preparation of Dihydrogen

(i) Typically, hydrogen is created when powdered zinc reacts with diluted hydrochloric acid.

Zn + 2H+ → Zn2+ + H2

(ii) Zinc and aqueous alkali can also be combined to create hydrogen. The reaction is given below:

Zn + 2NaOH → Na2ZnO2 + H2

2. Commercial Production of Dihydrogen

Below is a list of methods that are frequently used:

i) Using platinum electrodes, acidified water is electrolysed to produce hydrogen.

\(\begin{array}{l}2H_{2}O(l) \xrightarrow[\textup{Traces of acid/base}]{\textup{Electrolysis}} 2H_{2}(g) + O_{2}(g)\end{array} \)

Detailed Physical Properties of Hydrogen

  • It is a gas with no colour and odour and has the lowest density of all gases. It is seen as the clean fuel of the future, which is generated from water and returned to water when oxidized.
  • It is present in water and in almost all molecules in living things. It remains bonded with carbon and oxygen atoms. It can be said that it is the most abundant element in the universe.
  • It is present as a gas in the atmosphere in one part per million volumes. Hydrogen is spotless and is non-toxic and safe to produce from various different sources, transport, and store in large amounts.
  • It is named an energy carrier because it stores energy which is first created somewhere else.
  • This element was artificially produced in the 16th century. It was named as hydrogen whose Greek name is ‘water-former’

(ii) By electrolysing brine solution, it is produced as a byproduct in the production of sodium hydroxide and chlorine. The reactions that take place during electrolysis are:

At anode: 2Cl(aq) → Cl2(g) + 2e
At cathode: 2H2O(l) + 2e → H2(g) + 2OH(aq)

The overall reaction is

2Na+ (aq) + 2Cl (aq) + 2H2O(l) → Cl2 (g) + H2 (g) + 2Na+ (aq) + 2OH (aq)

Chemical Properties of Hydrogen

The following reactions can be used to demonstrate the chemistry of dihydrogen:

1. Reaction with X2 (Halogens): It produces hydrogen halides (HX) after reacting with halogens (X2).

X2(g) + H2(g) + → 2HX(g)

Where X = Cl, F, I, Br

2. Reaction with O2 (dioxygen): Water is created when it reacts with dioxygen. The reaction produces a lot of heat.

\(\begin{array}{l}2H_{2}(g) + O_{2}(g) \overset{\textup{catalyst or heating}}{\rightarrow} 2H_{2}O (l)\end{array} \)

3. Reaction with N2(dinitrogen): It forms ammonia with dinitrogen.

\(\begin{array}{l}3H_{2}(g) + N_{2}(g) \xrightarrow[Fe]{673K, 200 atm} 2NH_{3}(g)\end{array} \)

4. Reactions with metal oxides and metal ions: It reduces some metal oxides and metal ions in aqueous solutions into the appropriate metals.

For example, Pd2+(aq) + H2(g) → 2H+(aq) + Pd(s)

5. Reactions with metals (M): It reacts at a high temperature with various metals to produce the corresponding hydrides.

H2(g) + 2M(g) → 2MH(s)

Where M is an alkali metal.

Uses of Hydrogen

  • Ammonia synthesis is the most significant use of hydrogen.
  • A large amount of hydrogen is consumed in the catalytic hydrogenation of vegetable oils to extract solid fat.
  • It is also consumed as rocket fuel when combined with oxygen, and as a rocket propellant by nuclear energy.
  • Hydrogen is burnt as a fuel to burn in internal combustion engines.

Frequently Asked Questions – FAQs


Why does an electric arc require a high temperature to produce atomic hydrogen?

This is because the dissociation of dihydrogen into its atoms around 2000K is only 0.081% and rises to 95.5% at temperatures around 5000K. Additionally, due to the high H-H bond enthalpy, it is comparatively inert at ambient temperature.

Why does hydrogen combine with almost all the elements?

Since hydrogen has an incomplete orbital and an electronic configuration of 1s1, it can combine with practically every element. Reactions are carried out by
(i) Losing the single electron and producing H+.
(ii) Acquiring an electron to create H.
(iii) By sharing electrons to create a single covalent bond.

Who won the Nobel Prize for separating deuterium by physical methods?

Harold C. Urey, an American physicist, won the Nobel Prize in 1934 for physically isolating the hydrogen isotope (deuterium) with mass number 2.

Which hydrogen isotope is radioactive?

Only tritium is radioactive and emits low-energy β – particles.

What are the % abundance of hydrogen in the universe and the earth’s atmosphere?

Dihydrogen is the most prevalent element in the universe (it accounts for 70% of its total mass). It is substantially less common (0.15% by mass) in the earth’s atmosphere. However, it makes up 15.4% of the earth’s crust and seas when combined.

Related Elements

Nickel Neon Potassium Cobalt
Helium Copper Sodium Calcium
Lithium Zinc Magnesium Scandium
Beryllium Gallium Aluminum Titanium
Boron Germanium Silicon Vanadium
Carbon Arsenic Phosphorus Chromium
Nitrogen Selenium Sulfur Manganese
Oxygen Bromine Chlorine Iron
Fluorine Krypton Argon
Test your knowledge on Hydrogen


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