NCERT Handwritten Notes Alkanes [ Pdf Download ]


NCERT Handwritten Notes Alkanes [ Pdf Download ]

 Physics, Chemistry, Biology


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NCERT Handwritten Notes Alkanes Pdf Download



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What are Alkanes?

Alkanes are organic compounds made up of carbon and hydrogen atoms that are single-bonded. Alkanes have the formula CnH2n+2 and are split into three groups: chain alkanes, cycloalkanes, and branched alkanes.

Alkanes are a group of chemicals that possess single covalent connections between carbon and hydrogen atoms. This group of chemicals is made up of solitary covalent connections between carbon and hydrogen atoms. An analogous series with the chemical formula C nH2n+2 is also included.

Alkanes are the most basic family of compounds. They are made up entirely of carbon and hydrogen. Each carbon atom has four bonds, while each hydrogen atom has one. Chemists prefer line-angle formulas over condensed structural formulas because they are easier and faster to draw. Alkane structural formulas can also be written in a condensed form.


Methane is a simple alkane with one carbon atom and the chemical formula CH4. Because this molecule only has single covalent bonds, its structural formula is

alkanes METHANE
alkanes – METHANE


Additional carbon atoms are joined to each other in a long chain alkane molecule by a single covalent bond. Each atom is connected to four hydrogen atoms in order to form four single covalent connections. Octane is the name for this long-chain structure. The structural formula of an eight-carbon alkane is C 8H 18 and the molecular formula is C 8H 18.

alkanes - OCTANE
alkanes – OCTANE


Alkanes List

The following is a list of various Alkanes, along with their molecular formulas. ​

List of Alkanes  Molecular Formula  Structure
Methane (CH4)

alkanes - METHANE
alkanes – METHANE

Ethane (C2H6)

alkanes - Ethane
alkanes – Ethane

Propane (C3H8)

alkanes - Propane
alkanes – Propane

Butane (C4H10)

alkanes - Butane
alkanes – Butane

Pentane (C5H12)

alkanes - Pentane
alkanes – Pentane

Hexane (C6H14)

alkanes - Hexane
alkanes – Hexane

Heptane (C7H16)

alkanes - Heptane
alkanes – Heptane

Octane (C8H18)

alkanes - Octane
alkanes – Octane

Nonane (C9H20)

alkanes - Nonane
alkanes – Nonane

Decane (C10H22)

Physical Properties of Alkanes

1. The Solubility of Alkanes

  • Alkanes are often non-polar compounds due to the small difference in electronegativity between carbon and hydrogen and the covalent character of the C-C or C-H bond.
  • Polar molecules are soluble in polar solvents, while non-polar molecules are soluble in non-polar solvents, as we know. As a result, alkanes are hydrophobic, meaning they are water-insoluble.
  • They are soluble in organic solvents, however, because the energy required to overcome existing Van Der Waals forces and generate new ones is equal.

2. The Boiling Point of Alkanes

  • As the molecular size or surface area of the molecule increases, the intermolecular Van Der Waals forces rise as well.
  • The boiling point of alkanes rises as their molecular weight rises.
  • In comparison to their structural isomers, straight-chain alkanes appear to have a greater boiling point.

3. The Melting Point of Alkanes

  • The melting point of alkanes follows the same pattern as their boiling point: it rises as the molecular weight rises.
  • This is due to the fact that higher alkanes are solids, making intermolecular forces of attraction difficult to overcome.
  • Even-numbered alkanes have a higher melting point trend than odd-numbered alkanes, owing to the fact that even numbered alkanes pack well in the solid phase, generating a well-organized structure that is difficult to break.


Alkane Formula and Structure

Alkane structural formulas can be written in a condensed form. Pentane, for instance, has three CH2 methylene groups in the midst of its structural formula. We can put them in a group and create the structural formula for them. The formulas for the first five alkanes having an unbranched chain are listed below.

Name The molecular formula of alkane The condensed structural formula of alkane
Methane CH4 CH4
Ethane C2H6 CH3CH3
Propane C3H8 CH3CH2CH3
Butane C4H10 CH3(CH2)2CH3
Pentane C5H12 CH3(CH2)3CH3

Each vertex and line termination represents a carbon atom, and each line represents a bond in this shortened method of drawing structural formulas.

Alkane Formula Chemistry

Organic compound formulas provide information at various levels of sophistication. The number of each type of atom in a molecule of a substance is determined using molecular formulae, such as the one for octane.

The molecular formula C8H18 can refer to a variety of alkanes, each with its own set of chemical, physical, and toxicological characteristics. The structural formulae for these various compounds show the sequence in which the atoms in a molecule are organized. Structural isomers are compounds with the same molecular formula but distinct structural formulae.

Alkanes can be used to make almost any organic compound. Furthermore, many critical sections of organic compounds have one or more alkane groups bound as substituents onto the underlying organic molecule without a hydrogen atom. As a result of these considerations, alkanes are used in the names of numerous organic substances.

Branched Chain Alkane Formula

Alkanes’ carbon atoms can form straight chains, branching chains, or rings, just like other organic compounds. Straight chain alkanes, branched-chain alkanes, and cycloalkanes are the three types of alkanes. CnH2n+2 is the usual molecular formula for straight and branched-chain alkanes, while CnH2n is the formula for cyclic alkanes.


The four hydrocarbon molecules in the diagram, for example, each have eight carbon atoms. All of the carbon atoms in one of the molecules are in a straight chain, two of them are in branching chains, and six of them are in a ring in a fourth.

Alkyl Groups

When a halogen substituent attaches to an alkane molecule, one of the molecule’s carbon-hydrogen bonds is transformed to a carbon-substituent bond. It’s easier to understand with an example: when methane combines with chlorine, a new chemical called chloromethane is generated. The novel chemical is made comprised of a CH3 group bound to a chlorine atom.

Alkyl Groups
Alkyl Groups


An alkyl group is formed when hydrogen is removed from one of the alkane’s bonds. The letter R is often used to symbolize this Alkyl group, just as the letter X is used to indicate halogens. The following is a generalized methane chlorine reaction:

Alkyl Groups
Alkyl Groups


Frequently Asked Questions – FAQs

What are the first four alkanes?

The first four alkanes are methane (CH4), ethane (C2H6), propane (C3H8), and butane (C4H10). The simplest alkane is methane gas, which has the chemical formula CH4.

How are alkanes classified?

Alkanes are hydrocarbon atoms with only one link. Alkanes are divided into three categories: linear straight alkanes, branched alkanes, and cyclic alkanes.

Is alkane a functional group?

Alkanes aren’t usually thought of as functional groups; rather, they’re a type of compound that doesn’t have any. In an alkene, a functional group is a carbon-carbon double bond.

What is the general formula of alkyne?

Alkynes are compounds with the typical chemical formula CnH2n2 in a homologous series.

What is the simplest alkyne?

Alkynes are carbon-carbon hydrocarbons with three bonds. There is no geometric or optical isomerism in them. As seen on the right, ethyne (HCCH), often known as acetylene, is the simplest alkyne.



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