Properties of Hydrogen: What is the lightest element that has ever been discovered? In the contemporary periodic table, what is the first element? It is, in fact, hydrogen. Hydrogen is a colourless, tasteless, odourless gas and is highly flammable. It burns with oxygen and its flame is colourless and almost invisible. The flame temperature of hydrogen is very high. Water is formed as a byproduct when hydrogen and oxygen are burned together. Hydrogen exists as a gas at normal temperature and becomes liquid at minus 259.14 degrees centigrade.

In this article, you’ll learn about hydrogen’s occurrence, properties, and similarities to alkali metals and halogens, as well as its applications. Read on to find more!

Occurrence of Hydrogen

Hydrogen was first discovered by Henry Cavendish in 1766. In Greek, hydro means water, and gene mean producer. Hence Lavoisier named this element as hydrogen. Hydrogen exists in various forms like isotopes, allotropes, molecular and ionic forms.

Hydrogen is the most abundant element in the universe, accounting for around 70% of the total mass. The huge planets Jupiter and Saturn are primarily made up of hydrogen. About half of the mass of the sun and stars is hydrogen. It is the third most plentiful element on the planet’s surface. It makes up 15.4 per cent of the earth’s crust and seas when combined. Hydrogen is also found in water, coal, petrol, clay, and all other animal and vegetable matter.

Most of the hydrogen on our earth is found in the form of compounds. Hydrogen gas is very light, due to this it is found in very small quantities in the upper atmosphere of the earth, on earth it is found in the form of water (H₂O). Every molecule of water (H₂O) contains two atoms of hydrogen, in this way hydrogen is available in large quantities on earth in the form of water in oceans and rivers and in the form of ice on poles and mountains. And also present in the form of water in plants.

Hydrogen exists in atomic form only at high temperatures. The normal elemental form exists as a diatomic molecule, i.e., dihydrogen \({\rm{(}}{{\rm{H}}_{\rm{2}}}{\rm{)}}\).

Isotopes of Hydrogen

Isotopes are defined as atoms with the same number of protons but that have a different number of neutrons. Hydrogen exists in three isotopic forms, i.e., protium, deuterium, and tritium. The number of protons, electrons, caesium, and neutrons in three isotopic forms are summed up in the following table.

Name	Symbol	Atomic Number	Mass Number	Number of Electrons	Number of Protons	Number of Neutrons	Atomic Structure
Protium	\({}_1^1{\rm{H}}\) or \({\rm{H}}\)	\({\rm{1}}\)	\({\rm{1}}\)	\({\rm{1}}\)	\({\rm{1}}\)	\({\rm{0}}\)
Deuterium	\({}_1^2{\rm{H}}\) or \({\rm{D}}\)	\({\rm{1}}\)	\({\rm{2}}\)	\({\rm{1}}\)	\({\rm{1}}\)	\({\rm{1}}\)
Tritium	\({}_1^3{\rm{H}}\) or \({\rm{T}}\)	\({\rm{1}}\)	\({\rm{3}}\)	\({\rm{1}}\)	\({\rm{1}}\)	\({\rm{2}}\)

Protium: It is the simplest hydrogen molecule that is found in the largest amount, it has only one electron and one proton and it has no neutrons. It is the most abundant isotope of hydrogen. This occurs in natural hydrogen to the extent of 99.9844%.

Deuterium: Deuterium is 0.002 per cent of ordinary hydrogen molecules and it is a stable molecule. It was discovered by Harold Urey in 1932. This hydrogen molecule contains a neutron in addition to an electron and a proton. Due to having one neutron in it, it is twice as full as an ordinary hydrogen molecule, hence it is also called heavy hydrogen or deuterium. It reacts with oxygen to form heavy water (D₂O).

Tritium: Tritium is a very rare and radioactive hydrogen molecule. It consists of one electron, one proton and two neutrons. It is three times as heavy as an ordinary hydrogen molecule. It is an extremely unstable molecule.

How Do We Produce Hydrogen?

There are many methods of making hydrogen, some of which are as follows:

1. Hydrogen is obtained by the reaction of zinc and sulfuric acid.
2. Hydrogen is also obtained by the reaction of aluminum and sodium hydroxide.
3. Hydrogen is also obtained by the reaction of silicon and sodium hydroxide.
4. Hydrogen is also obtained by the electrolysis of water.
5. Hydrogen is formed as a byproduct when making sodium hydroxide from salt.

Unique Position of Hydrogen in the Periodic Table

Hydrogen is the first element in the periodic table with atomic number \({\rm{1}}\). It has one proton and one electron, and its electronic configuration is \({\rm{1}}{{\rm{s}}^{\rm{1}}}\). Hydrogen resembles both alkaline metal and halogen. Therefore, its position is anomalous and controversial. The main points of the resemblance of hydrogen with alkali metals and halogens are briefly discussed in the following content.

Resemblance with Alkaline Metal

Hydrogen resembles alkali metals, i.e., lithium \(\left( {{\rm{Li}}} \right)\), sodium \(\left( {{\rm{Na}}} \right)\), potassium \(\left( {{\rm{K}}} \right)\), rubidium \(\left( {{\rm{Rb}}} \right)\), caesium \(\left( {{\rm{Cs}}} \right)\), and francium \(\left( {{\rm{Fr}}} \right)\) of Group \({\rm{1}}\) of the periodic table in the following respects:

1. Electronic configuration: Like alkaline metals, hydrogen also contains one electron in the valence shell.
   \({\rm{H}}(1) – 1\;{{\rm{s}}^1}\)
   \({\rm{Li}}(3) – 1\;{{\rm{s}}^2},\,2\;{{\rm{s}}^1}\)
   \({\rm{Na}}(11) – 1\;{{\rm{s}}^2},\,2\;{{\rm{s}}^2},\,2{{\rm{p}}^6},\,3\;{{\rm{s}}^1}\)
   \({\rm{K}}(19) – 1\;{{\rm{s}}^2},\,2\;{{\rm{s}}^2},\,2{{\rm{p}}^6},\,3\;{{\rm{s}}^2},\,3{{\rm{p}}^6},\,4\;{{\rm{s}}^1}\)
2. Electropositive character: Hydrogen also loses its only electron to form hydrogen ion, i.e.,\({{\rm{H}}^{\rm{ + }}}\) (proton) as that of alkaline metals.
   \({\rm{H}} \to {{\rm{H}}^{\rm{ + }}}{\rm{ + }}{{\rm{e}}^{\rm{ – }}}\)
   \({\rm{Na}} \to {\rm{N}}{{\rm{a}}^{\rm{ + }}}{\rm{ + }}{{\rm{e}}^{\rm{ – }}}\)
3. Oxidation state: The compounds of hydrogen and alkaline metals show the same oxidation state i.e., \( + 1\).
   Example: Hydrogen chloride \(\left( {{{\rm{H}}^{\rm{ + }}}{\rm{C}}{{\rm{l}}^{\rm{ – }}}} \right)\), sodium chloride \(\left( {{\rm{N}}{{\rm{a}}^ + }{\rm{C}}{{\rm{l}}^ – }} \right)\) and potassium bromide \(\left( {{{\rm{K}}^{\rm{ + }}}{\rm{C}}{{\rm{l}}^{\rm{ – }}}} \right)\).
4. Reaction with Non-metals: Hydrogen combines with electronegative elements, i.e., non-metals such as oxygen, halogen, and sulfur forming oxides, halides, and sulfides, respectively, as similar to the alkaline metals.
   Oxide: \({{\rm{H}}_2}{\rm{O}}\) like \({\rm{N}}{{\rm{a}}_2}{\rm{O}},\,{{\rm{K}}_2}{\rm{O}}\), etc.
   Halides: \({\rm{HCl}}\) like \({\rm{NaCl, KCl}}\), etc.
   Sulfides: \({{\rm{H}}_2}{\rm{S}}\) like \({\rm{N}}{{\rm{a}}_2}\;{\rm{S}},\;\,{{\rm{K}}_2}\;{\rm{S}}\), etc.
5. Reducing Nature: Like alkaline metals, hydrogen also acts as a strong reducing agent.
   Example: On heating, \({\rm{F}}{{\rm{e}}_3}{{\rm{O}}_4} + 4{{\rm{H}}_2} \to 3{\rm{Fe}} + 4{{\rm{H}}_2}{\rm{O}}\)
   On heating, \({{\rm{B}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}{\rm{ + 6K}} \to {\rm{2B + 3}}{{\rm{K}}_{\rm{2}}}{\rm{O}}\)

Characterstics of Hydrogen Vs Alkali Metals

Apart from the above similarities, hydrogen also differs from alkali metal in the following characteristics:

1. Alkali metals are typical metals, while hydrogen is non-metal.
2. Hydrogen is diatomic, while alkali metals are monoatomic in nature.
3. The ionization enthalpy of hydrogen is very high as compared to alkaline metals.
4. Compounds of hydrogen are mainly covalent (like \({\rm{HCl}},\,{{\rm{H}}_2}{\rm{O}}\) etc.), while those of alkaline metals are ionic (like \({\rm{NaCl, KF}}\), etc.).

Resemblance with Halogen

Hydrogen resembles halogens, i.e., fluorine \(\left( {\rm{F}} \right)\), chlorine \(\left( {\rm{Cl}} \right)\), bromine \(\left( {\rm{Br}} \right)\), and iodine \(\left( {\rm{l}} \right)\) of group \(17\) of the periodic table in the following respects:

1. Electronic configuration: Like halogens, hydrogen also needs one electron to attain the nearest inert (noble) gas configuration, i.e., helium.
Example: Hydrogen \(\left( {{\rm{H}},{\mkern 1mu} \,1{{\rm{s}}^1}} \right)\) has one electron less than next noble gas helium \(\left( {{\rm{He}},{\mkern 1mu} \,1{{\rm{s}}^2}} \right)\), similarly fluorine \(\left( {{\rm{F,}}\,{\rm{1}}{{\rm{s}}^{\rm{2}}}{\rm{,}}\,{\rm{2}}{{\rm{s}}^{\rm{2}}}{\rm{,}}\,{\rm{2}}{{\rm{p}}^{\rm{5}}}} \right)\) has one electron less than next noble gas neon \(\left( {{\rm{Ne}},{\mkern 1mu} \,1{{\rm{s}}^2},{\mkern 1mu} \,2{{\rm{s}}^2},{\mkern 1mu} \,2{{\rm{p}}^6}} \right).\)

2. Electronegative character: Halogens gain one electron and form halide. Similarly, hydrogen also gains one electron to form a hydride \({\rm{(}}{{\rm{H}}^{\rm{ – }}}{\rm{)}}\) ion.
\({\rm{H + }}{{\rm{e}}^{\rm{ – }}} \to {{\rm{H}}^{\rm{ – }}}\)
\({\rm{Cl + }}{{\rm{e}}^{\rm{ – }}} \to {\rm{C}}{{\rm{l}}^{\rm{ – }}}\)

3. Ionization enthalpy: The ionization enthalpy of hydrogen is quite comparable with those of halogen but much higher than those of alkaline metals.

Element	Ionisation enthalpy in \({\rm{kJ}}/{\rm{mol}}\)
\({\rm{H}}\)	\(1312\)
\({\rm{F}}\)	\(1681\)
\({\rm{Cl}}\)	\(1255\)
\({\rm{Li}}\)	\(520\)
\({\rm{Na}}\)	\(496\)
\({\rm{K}}\)	\(419\)

4. Oxidation state: Similar to the halogen, hydrogen also shows a \({\rm{ – 1}}\) oxidation state.
Example: With sodium compounds like sodium hydride \(\left( {{\rm{N}}{{\rm{a}}^ + }{{\rm{H}}^ – }} \right)\) and sodium chloride  \(\left( {{\rm{N}}{{\rm{a}}^{\rm{ + }}}{\rm{C}}{{\rm{l}}^{\rm{ – }}}} \right)\).

5. Atomicity and non-metallic character: Just like halogen, hydrogen also exists as a diatomic molecule, i.e., \({{\rm{H}}_{\rm{2}}},\,{{\rm{F}}_{\rm{2}}},\,{\rm{C}}{{\rm{l}}_{\rm{2}}}\) etc. Like halogen, hydrogen is also non-metal.

6. Reaction with metals: Both hydrogen and halogens combine with an alkali metal and alkaline earth metals give respective metallic hydride and metallic halide, respectively.
Example: Reaction with alkali metals
\(2{\rm{Na}} + {{\rm{H}}_2} \to 2{\rm{NaH}}\)
\(2{\rm{Na}} + {\rm{C}}{{\rm{l}}_2} \to 2{\rm{NaCl}}\)

7. Formation of covalent compounds: Like halogens, hydrogen readily combines with non-metals such as carbon, silica, nitrogen, etc., to form covalent compounds.
Example: Covalent compounds of hydrogen are methane \({\rm{(C}}{{\rm{H}}_{\rm{4}}}{\rm{)}}\), silane \({\rm{(Si}}{{\rm{H}}_{\rm{4}}}{\rm{)}}\), and ammonia \({\rm{(N}}{{\rm{H}}_{\rm{3}}}{\rm{)}}\). Covalent compounds of halogen are carbon tetrachloride \({\rm{(CC}}{{\rm{l}}_{\rm{4}}}{\rm{)}}\), silicon tetrachloride \({\rm{(SiC}}{{\rm{l}}_{\rm{4}}}{\rm{)}}\), and nitrogen trichloride \({\rm{(NC}}{{\rm{l}}_{\rm{3}}}{\rm{)}}\).

Difference Between Hydrogen and Halogen

After having so many similarities between hydrogen and halogen, hydrogen also shows some of the following differences.

1. In molecular form, the hydrogen atom does not have any unshared electron pair, while halogen atoms have three unshared pairs of electrons.
2. Halogens readily form halide ions but hydrogen forms hydride ions only in compounds with alkali and alkaline earth metals.
3. The oxides of halogens are generally acidic, while that of hydrogen is neutral.

What is Ortho and Para Hydrogen?

A molecule of dihydrogen contains two atoms. The nuclei of both the atoms in each molecule of dihydrogen are spinning. Depending upon the direction of the spin of the nuclei, hydrogen is of two types.

1. Ortho hydrogen: Molecules of hydrogen in which spins of both the nuclear are in the same direction (parallel nuclear spins).
2. Para hydrogen: Molecule of hydrogen in which spins of both the nuclear are in the opposite direction (antiparallel nuclear spin).

At room temperature, ordinary dihydrogen contains \(75\% \) of ortho hydrogen and \(25\% \) of parahydrogen. At the liquid air temperature \(\left( {77\,{\rm{ K}}} \right),\) it is \(1:1\), and at about \(20\,{\rm{K}},\) it is pure para hydrogen.

Hydrogen Bonding

The attractive force which binds the hydrogen atom of one molecule with an electronegative atom like fluorine, oxygen and the nitrogen of another molecule is known as a hydrogen bond. A hydrogen bond is weaker than a covalent bond.

To form a hydrogen bond, the molecule must contain a hydrogen atom attached to the highly electronegative atom, and the size of the electronegative atom should be quite small.

The hydrogen bonding is usually observed in hydrogen fluoride \(\left( {{\rm{HF}}} \right)\), water \({\rm{(}}{{\rm{H}}_{\rm{2}}}{\rm{O)}}\), ammonia \({\rm{(N}}{{\rm{H}}_{\rm{3}}}{\rm{)}}\), the carboxylic acid \(\left( {{\rm{RCOOH}}} \right)\), alcohol \(\left( {{\rm{ROH}}} \right)\), amines \({\rm{(RN}}{{\rm{H}}_{\rm{2}}}{\rm{)}}\), etc.

Hydrogen Peroxide

Hydrogen peroxide was discovered by French chemist J.L Thenard. It is the simplest member of the class of peroxides. Its molecular formula is \({{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}\). Hydrogen peroxide is a pale blue colour in concentrated form. It is an odourless, thick syrupy liquid. It is a strong oxidizer. It must be kept in wax-lined coloured bottles to avoid decomposition into water and oxygen.

Hydrogen peroxide is a non-planar molecule, and two oxygen atoms are bonded together through a peroxide bond. It has an open book structure. Each oxygen atom is further attached to a hydrogen atom through a single bond.

Uses of Hydrogen

Hydrogen naturally exists as a diatomic molecule, i.e., dihydrogen. Some of the important uses of hydrogen are:

1. It is used for the preparation of useful compounds like ammonia, water gas, methyl alcohol, etc.
2. It is used in the hydrogenation of oils for preparing vanaspati ghee.
3. Atomic hydrogen torch is used for welding purposes.
4. Rocket fuel comprises both liquid hydrogen and liquid oxygen.
5. It is used as an excellent reducing agent in metallurgy.
6. Hydrogen is used as a source of electricity.

Summary

In this article, you have gained knowledge regarding hydrogen, its occurrence, position of hydrogen in the modern periodic table, properties of hydrogen similar to alkali metal and halogen, uses, etc.

FAQs

Q.1. What are the properties of hydrogen sulfide?
Ans: Hydrogen sulfide is colourless, poisonous gas having the odour of a rotten egg. It is produced by the decomposition of organic matter by microorganisms in the absence of oxygen.

Q.2. What are the properties of hydrogen chloride?
Ans: Hydrogen chloride is a gas with a pungent odour and has a pale yellow colour. It is diatomic and covalent.

Q.3. What are the five physical properties of hydrogen?
Ans: Hydrogen is colourless, odourless, tasteless, non-metallic diatomic gas. It is a highly combustible gas.

Q.4. What are the properties and uses of hydrogen?
Ans: Hydrogen is colourless, odourless, tasteless, non-metallic diatomic gas. It shows both electropositive and electronegative properties. It has high ionization enthalpy. It forms covalent compounds and acts as a good reducing agent. It exhibits both +1 and -1 oxidation states.
Some of the uses of hydrogen are for preparing compounds like ammonia, water gas, etc., rocket fuel, hydrogenation of oil, welding purposes, etc.

Q.5. What are the two properties of pure hydrogen?
Ans: Pure hydrogen exists as a dihydrogen molecule. It is a highly combustible gas.

Q.6.What are the physical and chemical properties of hydrogen?
Ans: The physical properties of hydrogen: It is a colourless, odourless, tasteless, non-metallic diatomic gas.
The chemical properties of hydrogen: It shows both electropositive and electronegative properties.
Hydrogen reacts with an alkali metal, and alkaline earth metals give metal hydrides.
Reaction with alkali metals.
2Na+H2→2NaH2Na+H2→2NaH
Hydrogen is a good reducing agent.
Fe3O4+4H2→3Fe+4H2O

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