Hydrogen

HYDROGEN

• Symbol: H
• Atomic Number: 1
• Atomic mass: 1.0078 amu
• Nature: s-block element
• Electronic Configuration: 1s¹
• Electronic Structure:
  
  

Discovery Of Hydrogen:
The discovery of hydrogen is credited to the British scientist Henry Cavendish in 1766. Cavendish isolated hydrogen gas by reacting metals with acids, leading to the identification of hydrogen as a distinct element. This discovery laid the foundation for further research and understanding of the properties and uses of hydrogen in various fields.

Position Of Hydrogen In The Periodic Table:
Elements in modern periodic table are arranged on the basis of their electronic configuration and to some extent on the basis of their properties.
Hydrogen is a unique element in the periodic table due to its properties and characteristics. It is partially resemble with the elements of Group IA (alkali metals), Group IVA (Carbon family)and with Group VIIA (Halogen), but does not resemble complete with any of the groups.

The different behaviour of hydrogen is because of its simplest atom which possesses a singly positive charged nucleus and one electron moving around the nucleus. It is typically placed at the top of Group 1A in the periodic table, above lithium, even though it is not a metal like the other elements in Group 1A. Its placement in the periodic table is a subject of debate among chemists and scientists.

Hydrogen And Alkali Metals:
Hydrogen resembles with alkali metals only in possessing one electron in the s-orbital of the outermost shell (valence shell).
Hydrogen is often considered separately from the alkali metals due to its distinct properties, such as being a diatomic gas at room temperature and is also a non-metal. It does not lose its valence electron and does not form H⁺ ion like Na⁺ because the valence electron in hydrogen is strongly attracted by the positively charged nucleus.
Although it forms compounds with non-metals such as HF, HCl etc and their aqueous solutions, ionize to form hydrogen cation.

(HCl ⇌ H⁺ + Cl^-)

but these H⁺ ions or protons unlike Na⁺ do not exist free in water except in the solvated form such as H₃⁺O.

Hydrogen And Carbon Family:
It resembles with carbon and its family members (group IVA) in that the valence shell of hydrogen is half filled. Some thermodynamic properties such as ionization potential, electron affinity values etc of hydrogen are also similar to that of carbon and other members of its family.
However hydrogen differs in many respects from the members of carbon family. It is a gas. It shows monovalency and its valence shell consists of "s" orbital where as members of carbon family are solids. They show tetra valency and their valence shell consists of s and p orbitals.

Hydrogen And Carbon Family:
Hydrogen also resembles with halogens in that it is a non-metal and forms H^- ion by gaining electron from strong electro-positive metals. Thus Na⁺, H^-and Na⁺ Cl^- are comparable. It is also a gas consisting of diatomic molecules (H₂) like F₂, and Cl₂.
However, it differs from halogens in that unlike Cl^-, H^- is incapable of existence in water since H₂, is formed immediately and there is no stabilization due to solvation. Electron affinity of hydrogen is also much less than halogens.

Preparation Of Hydrogen:
LABORATORY PREPARATION:
Hydrogen gas can be prepared in the laboratory through various methods. One common method is the reaction of a metal with an acid.
For example:
(i) Zinc can react with hydrochloric acid to produce hydrogen gas:

Zn(s) + 2HCl(aq) ⟶ ZnCl_2(aq) + H_2(g)

(ii) Another method is the electrolysis of water, where an electric current is passed through water to split it into hydrogen and oxygen gases:

2H₂O_(l) ⟶ 2H_2(g) + O_2(g)

INDUSTRIAL PREPARATION OF HYDROGEN:
In industrial settings, hydrogen gas is primarily produced through the following methods:
(i) Steam reforming:
This is the most common method of industrial hydrogen production, where natural gas (methane) is reacted with steam in the presence of a catalyst (Nickel) to produce Water gas (Mixture of hydrogen and carbon monoxide). The water-gas shift reaction is then used to convert the carbon monoxide into additional hydrogen:

OR

CH₄ + H₂O ⟶ CO + 3H₂ (Water gas)

CO + H₂O ⟶ CO₂ + H₂

(ii) Partial oxidation:
In this process, a hydrocarbon fuel such as natural gas or oil is partially oxidized with oxygen or air to produce hydrogen gas and carbon monoxide:

CH₄ + ½O₂ ⟶ CO + 2H₂

(iii) Electrolysis of water:
In some cases, electrolysis of water is used in industrial settings to produce hydrogen gas by passing an electric current through water to split it into hydrogen and oxygen gases. Hydrogen collects at cathode and oxygen gas, a by-product is collected at anode.

2H₂O_(l) ⟶ 2H_2(g) + O_2(g)

These methods are commonly used in industrial processes to produce large quantities of hydrogen gas for various applications.

(iv) Action Of Steam On Coal:
when steam is passed over red hot coke at about 1000 ℃, a mixture of hydrogen and carbon monoxide (water gas) is formed.

Hydrogen is obtained in free form by removing carbon monoxide from water gas. It is done by heating the mixture of two gases with more steam at 500 ℃ in the presence of catalyst (iron oxide or cobalt oxide). As a result carbon monoxide is changed to carbon dioxide which can easily be separated by dissolving in water under high pressure leaving behind free hydrogen gas.

(v) Steam with methanol:
A mixture of steam and vapours of methanol when heated at 250 ℃, produces mixture of hydrogen gas and carbon dioxide.

CH₃OH_(g) + H₂O_(g) ⟶ CO_2(g) +3H_2(g)

(vi) Thermal decomposition Of Hydrocarbon:
When natural gas (contain 94.60% methane) is heated in the absences of oxygen, It is decomposed into its components.

CH_4(g) ⟶ C_(l) + 2H_2(g)

This carbon obtained is known as carbon black.

(vii) Thermal Decomposition Of Ammonia:
Liquid ammonia is vapourized and passing over an active catalyst by heating at 1000 ℃.

The mixture of nitrogen and hydrogen gas is cooled to -196 ℃, nitrogen becomes liquid and free hydrogen gas is obtained.

Physical Properties Of Hydrogen:

• Hydrogen is the lightest and most abundant element in the universe.
• It is a colorless, odorless, and tasteless gas at room temperature.
• Hydrogen is highly flammable and burns with a pale blue flame.
• It has a low density and is non-toxic.
• Hydrogen is a non-metal and is a diatomic molecule, meaning it exists as (H₂) molecules in its natural state.
• It has a boiling point of -252.87°C and a melting point of -259.16°C.

Chemical Properties Of Hydrogen:
Hydrogen is highly reactive and has the ability to form compounds with a wide range of elements, making it a versatile element in chemical reactions.
Some common chemical reactions involving hydrogen include:
1. Combustion:
Hydrogen reacts with oxygen to form water in a highly exothermic reaction:

2H₂ + O₂ ⟶ 2H₂O

2. Hydrogenation:
Hydrogen can add to unsaturated compounds, such as alkenes, in a process known as hydrogenation. For example:

H₂ + C₂H₄ ⟶ C₂H₆

3. Acid-base reactions:
Hydrogen can act as a proton donor in acid-base reactions. For example, in the reaction of hydrogen chloride with water:

HCl + H₂O ⟶H₃O+ + Cl^-

These are just a few examples of the chemical reactions that involve hydrogen. Its reactivity and versatility make it a key element in various chemical processes.


Nascent Hydrogen:
Nascent hydrogen refers to hydrogen in its atomic form, rather than in its usual diatomic molecular form (H₂). Nascent hydrogen is highly reactive and is often used in organic chemistry reactions as a reducing agent. It is generated in situ by the reaction of a metal with an acid, such as zinc with hydrochloric acid. Nascent hydrogen is known for its ability to add to unsaturated compounds, facilitating various chemical transformations.

Isotopes Of Hydrogen:
Hydrogen has three isotopes: protium, deuterium, and tritium.
1. Protium (symbol: ₁H¹) :
is the most common and abundant isotope of hydrogen, making up about 99.98% of naturally occurring hydrogen. It consists of a single proton and no neutrons.

2. Deuterium (symbol: ₁H² or D):
is a stable isotope of hydrogen that contains one proton and one neutron. Deuterium is used in nuclear reactors and as a tracer in chemical reactions.

3. Tritium (symbol: ₁H³ or T):
is a radioactive isotope of hydrogen that contains one proton and two neutrons. Tritium is used in nuclear fusion reactions and as a tracer in biological and environmental studies.

These isotopes of hydrogen have different properties and applications based on their atomic structure and stability.

Use Of Hydrogen:
Hydrogen has various uses across different industries and applications. Some common uses of hydrogen include:

1. Energy production: Hydrogen can be used as a clean and renewable energy source in fuel cells to generate electricity with water as the only byproduct.
2. Industrial processes: It is commonly found in water molecules (H₂O) and plays a crucial role in various chemical reactions and industrial processes.
   Hydrogen is used in the production of ammonia for fertilizers, in petroleum refining, and in the production of methanol.
3. Food industry: Hydrogen is used in the hydrogenation of oils and fats to produce margarine and other food products.
4. Electronics: Hydrogen is used in the production of semiconductors and flat-panel displays.
5. Aerospace: Hydrogen is used as a propellant in rockets and spacecraft due to its high energy content and light weight.
   
   

These are just a few examples of the diverse applications of hydrogen in various industries.