CBSE Class 11th Hydrocarbons

Since the term "hydrocarbon" is derived from the words "hydro" and "carbon," where "hydro" denotes hydrogen elements and "carbon" denotes carbon elements, it is simple to describe hydrocarbons as compounds comprised only of hydrogen and carbon molecules. 
Both circular and straight-chain hydrocarbon configurations are possible. These hydrocarbons are utilized to create new materials using an alternative method.
Alkanes, alkenes, alkynes, and aromatic hydrocarbons are the four subclasses of hydrocarbons. The structures of alkanes, alkenes, alkynes, and aromatic hydrocarbons are either simple or rather complex. The synthesis of additional functional groups and their chemical properties can be learned from studying hydrocarbons.

Classification of hydrocarbons:

The area of science known as organic chemistry examines the structures, behaviors, and physical and chemical characteristics of organic substances that have covalent bonds—a type of chemical bond in which atoms share electrons—and carbon atoms.
Hydrocarbons are any class of organic chemical compounds consisting only of the elements hydrogen (H) and carbon (C). The structure of the complex is formed by the bonds formed by the carbon atoms, to which the hydrogen atoms attach themselves in various ways. The majority of natural gas and petroleum are composed of hydrocarbons. In addition to being employed as industrial chemicals, solvents, fibers, rubbers, fuels, and lubricants, they are also used as raw materials for plastics and explosives.

These compounds have the chemical formula CxHy. Trees and plants both contain hydrocarbons. Carrots and green leaves, for instance, are rich in carotenes, an organic pigment. Hydrocarbons exist in nature in a variety of forms. For example, fossil fuels, which include kerosene, compressed natural gas (CNG), liquefied petroleum gas (LPG), crude oil, and petroleum, all contain hydrocarbons. This indicates that hydrocarbons are an excellent energy source.

Properties of hydrocarbons:
The size of the hydrocarbon molecules has an impact on their melting and boiling points. Because of this, certain hydrocarbons are gases at room temperature, while others are liquids or solids.
They are made up of robust hydrogen-carbon bonds.
Strong molecular forces of attraction exist in molecules.
The lack of oppositely charged sides in hydrocarbon molecules is referred to as non-polarity. They are thus polar chemicals that are insoluble in water. In contrast, hydrocarbons are inherently inclined to reject water. For this reason, they are present in floor wax and related products.

Types of hydrocarbons:

In the past, chemists classified hydrocarbons as aromatic or aliphatic. The hydrocarbons were categorized using their sources and properties. Consequently, it was found that although aromatic hydrocarbons included components created by the chemical breakdown of plant extracts, aliphatic hydrocarbons were formed by the chemical degradation of fats or oils. Instead of classifying hydrocarbons according to their place of origin, we now do so based on their structure.

Saturated Hydrocarbons:

We refer to saturated hydrocarbons as alkanes. Single carbon-carbon and carbon-hydrogen bonds can be found in these hydrocarbons. In nature, these hydrocarbons form open chain formations. There are no double or triple bonds in these hydrocarbons. The simplest hydrocarbons are those that are saturated. CnH2n+2 is the general formula for saturated hydrocarbons.

Saturated Hydrocarbons' Physical Characteristics (Alkanes):

In nature, saturated hydrocarbons, also known as alkanes, are colorless and odorless.
Alkanes are molecules without polarity.
The gaseous phase is home to the first four alkanes. The remaining thirteen members, numbered from 5 to 17, are in the liquid phase.
In nature, alkanes with more than 18 carbon atoms are solid.
Alkanes include van der Waals forces between molecules. Higher boiling temperatures are found in alkanes with stronger van der Waals interactions between molecules.
Alkane melting points resemble boiling points for the same reason as previously mentioned. In other words, the melting point increases with molecule size (all other things being equal).

Saturated Hydrocarbons' Chemical Characteristics (Alkanes):

Alkanes react with oxygen on heating to produce water and carbon dioxide. First, let's heat methane (CH4), the first alkane.

CH4(gas) + 2O2(gas) → CO2(gas) + 2H2O(liquid)

Halogenation is the process of creating new compounds by substituting hydrogen atoms with halogen groups such as fluorine, chlorine, bromine, or iodine. When sunlight is present, the halogenation process takes place.

CH4 + Cl2 → CH3Cl (Chloromethane) + HCl

The isomerization and reformation procedures of straight-chain alkanes are carried out under heat in the presence of a platinum catalyst. Alkanes undergo isomerization to create branched-chain isomers. Hydrogen is released as a consequence of the reformation of the alkanes into cycloalkanes or aromatic hydrocarbons. These two techniques raise the octane number of the material. Because it generates a lot of branched alkanes with high octane values, butane is the most often isomerized alkane.

Preparation of Saturated Hydrocarbons (Alkanes): Alkanes can be made in a variety of ways, some of which are listed below:
From unsaturated fatty acids: Alkenes or alkynes, which are unsaturated hydrocarbons, can be transformed into alkanes by adding hydrogen gas while a catalyst (such as nickel) is present. This process of alkane creation is called hydrogenation. 

C2H4 (Ethene) + H2  → C2H6 (Ethane)

From alkyl halides: Alkyl halides can also be used to prepare alkanes through a hydrogen-zinc reaction.

CH4 (Methane) + HCl from CH3Cl + H2 Zn

Unsaturated Hydrocarbons:

Unsaturated hydrocarbons are organic compounds with a double or triple bond between two neighboring carbon atoms that are entirely made of hydrogen and carbon atoms. While alkynes are hydrocarbons with a triple bond between carbon atoms, alkenes are hydrocarbons with at least one double bond between two neighboring carbon atoms. The chemical formulae of unsaturated and saturated hydrocarbons differ, as may be seen below.

Unsaturated Hydrocarbons are of two types

• Alkenes

• Alkynes

Alkenes: Alkenes are a component of unsaturated hydrocarbons. Since alkenes are substances that create oil, they are referred to as olefins. These hydrocarbons have at least one double bond in addition to single carbon-carbon and carbon-hydrogen bonds. These hydrocarbons naturally form open chain structures as well.

CnH2n is the general formula for alkenes.

Physical Properties of Alkenes:

1. Ethene is the only unsaturated hydrocarbon (alkene) that has a pleasant scent; all other alkenes are colorless and odorless.
2. Comparatively speaking, alkenes smell stronger than alkanes.
3. Alkenes possess polarity.
4. Molecular mass determines the physical state: at room temperature, the simplest alkenes are gases, just like the corresponding saturated hydrocarbons.
5. The gaseous phase is home to the first three alkene components.
6. The following fourteen, numbered fourth through seventeenth, are in the liquid phase.
7. In nature, alkenes with more than 14 carbon atoms are solid.
8. Their melting and boiling points are high.

Chemical Properties of Alkenes:

Because alkenes can conduct addition processes, they can combine with hydrogen atoms to create other alkanes.
C2H4 (Ethene) + H2  → C2H6 (Ethane)

With the exception of iodine, which does not exhibit an addition reaction, hydrogen atoms can be substituted with halogen groups such as fluorine, chlorine, or bromine to generate new compounds known as dihalides.
C2H4 (Ethene) + Br2  → C2H4Br2 (Dibromoethane)

Preparation of Alkenes:
Alkenes can be made in a variety of ways, some of which are listed below:
From Alkynes: Lindlar's Catalyst, a catalyst similar to palletized charcoal, can be used to create unsaturated hydrocarbons (also known as alkenes) from alkynes by adding hydrogen gas.

C2H2 (Ethyne) + H2 Pd/C→ C2H4 (Ethene)

From alkyl halides: 
Alkenes can also be made from alkyl halides by heating them, while potash is dissolved in alcohol. This process eliminates the halogen molecule from the alkyl halides.
C2H5Cl → C2H4 (Ethene)

Alkynes:
There are alkynes in unsaturated hydrocarbons as well. These hydrocarbons have at least one triple bond between two carbon atoms in addition to single bonds of carbon to carbon and carbon to hydrogen. These hydrocarbons naturally form open chain structures as well. Ethyne, sometimes referred to as acetylene, is the first alkyne series member.

CnH2n-2 is the general formula for alkynes. 

Physical properties of alkynes:

1. With the exception of ethylene, which has an odor, unsaturated hydrocarbons, or alkynes, are colorless and odorless in nature.

2. Molecularly, alkynes are polar.

3. The gaseous phase is home to the first three alkynes.

4. The liquid phase is home to the next eight individuals, numbered fourth through eleventh.

5. In nature, alkynes with more than 11 carbon atoms are solid.

Chemical Properties of Alkynes:

1. Due to their triple bond, alkynes have the propensity to combine two molecules of hydrogen, halogen, or hydrogen halides to produce new compounds. This is why alkynes exhibit addition reactions in the same way as alkenes.

2. Water does not react with alkynes.

3. Alkynes demonstrate the ability to polymerize into long-chain carbon molecules.

Preparation of alkynes:
Alkynes can be made in a variety of ways, some of which are listed below:
By adding water to calcium carbide, alkynes such as ethyne and calcium hydroxide are formed, which can then be used to prepare further alkynes.

CaC2 + 2H2O  → Ca(OH)2 + C2H2 (Ethyne)

Vicinal dihalides can be converted into alkynes by reacting them with alcoholic potash, which removes one halogen molecule from the dihalide to generate alkenyl halide, which can subsequently be reduced to the alkyne.

Aromatic Hydrocarbons:
Aromatic substances have a nice fragrance since the word aromatic derives from the word aroma, which means pleasant smell. Another name for these hydrocarbons is Arenes. Benzenoids are the term for the majority of aromatic hydrocarbons since they have benzene rings in them. Non-Benzenoids are another name for certain aromatic hydrocarbons that do not have benzene rings.

Physical Properties of Aromatic Hydrocarbons:

1. These substances are aromatic, meaning that resonance provides extra stability. The ratio of carbon atoms to hydrogen atoms in these compounds is rather high.

2. There are two phases for aromatic hydrocarbons: gaseous and liquid.

3. Natural aromatic hydrocarbons have no color.

4. In water, aromatic hydrocarbons are insoluble.

Chemical Properties of Aromatic Hydrocarbons:

1. Aromatic hydrocarbons are able to perform Electrophilic Substitution Reactions.
2. Under some conditions, these hydrocarbons can also show addition and oxidation reactions.
3. When aromatic hydrocarbons are burned, they produce a yellow, sooty blaze.
4. Preparation of Aromatic Hydrocarbon

Reduction of Phenol: Zinc dust is used to reduce phenol, which is how aromatic hydrocarbons like benzene are made.

C6H6OH (Phenol) + Zn  → C6H6 (Benzene) + ZnO

Decarboxylation of aromatic acids: Benzene and other aromatic hydrocarbons can be made by heating benzoic acid sodium salt.

C6H6COONa + NaOH  CaO→ C6H6 (Benzene)+ Na2CO3

Applications for Hydrocarbons:

1. Paints employ hydrocarbons as solvents.
2. The lube and grease industries also use them.
3. Hydrocarbons are used in several medication manufacturing processes.
4. Many kinds of polymers are synthesized using hydrocarbons.
5. The main component of fuels is hydrocarbon.
6. Methane is the main component of natural gas.
7. Either ethylene and propylene or syngas are produced from ethane and propane.

FAQ-
Q.1 What are hydrocarbons?
Ans. Hydrocarbons are organic compounds made up of hydrogen and carbon atoms. They are the fundamental constituents of crude oil, natural gas, and petroleum products.
Q.2 What are the main sources of hydrocarbons?
Ans. Hydrocarbons are primarily derived from fossil fuels such as petroleum, coal, and natural gas. They can also be found in biomass and various organic materials.
Q.3 What are the different types of hydrocarbons?
Ans. Hydrocarbons are broadly categorized into two main types: aliphatic hydrocarbons and aromatic hydrocarbons. Aliphatic hydrocarbons include alkanes, alkenes, and alkynes, while aromatic hydrocarbons include benzene and its derivatives.
Q.4 How are hydrocarbons used in daily life?
Ans. Hydrocarbons play crucial roles in various aspects of daily life. They are used as fuels for transportation, heating, and electricity generation. Additionally, hydrocarbons serve as raw materials in the production of plastics, solvents, lubricants, and numerous other industrial products.
Q.5 Are hydrocarbons harmful to the environment?
Ans. While hydrocarbons are essential for modern society, their combustion releases carbon dioxide and other greenhouse gases, contributing to climate change. Moreover, accidental spills or leaks of hydrocarbons can cause environmental pollution, impacting ecosystems and human health.