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Chemistry > Hydrocarbons > Alkanes
Hydrocarbons

Alkanes

Alkanes are saturated hydrocarbons. By saturated hydrocarbons, it means alkanes have single hydrogen and carbon atoms in their chemical formula. Formula of alkane is CnH2n+2. Methane, propane, ethane, and butane are four alkanes. Let us learn in detail about Alkanes and their physical properties below.

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Hydrocarbons

Let us first begun by understanding what are hydrocarbons. Hydrocarbons are compounds that are made up of atoms of carbon and hydrogen exclusively. The unique nature of the carbon ensures that it shares a strong covalent bond with hydrogen. Since carbon atoms will make long chains with relative ease, hydrocarbons can be very big molecules linking even hundreds of atoms.

Actually, all living things or things that were once alive are actually made up of hydrocarbons. Some other most common examples are fossil fuels, natural gas, coal, petrol, and even the butter and cooking oil we use.

Broadly there are two types of hydrocarbons, namely saturated and unsaturated. Saturated hydrocarbons have a single bonding between their atoms. Which means only one pair of electrons is shared between any two atoms of the compound. Unsaturated hydrocarbons can have double or triple bonds.

Browse more Topics under Hydrocarbons

Alkanes Definition and Formula

Alkanes are another name of saturated hydrocarbons. This means they only have carbon and hydrogen atoms in their chemical formula. And these atoms are bonded by single bonds only. That means all atoms share only one pair of electrons with each other.

The general formula for alkanes is CnH2n+2

Here n is the number of atoms of carbon in their chemical structure. So accordingly the number of hydrogen atoms is 2n+2. This chemical formula will stand true for all saturated hydrocarbons.

Methane Alkanes

The simplest alkane is methane which is CH4. Here one atom of carbon is bonded to four atoms of hydrogen with single bonds. So the four valence electrons of carbon will bond with the one valence electron of each hydrogen atom. And so a completely saturated hydrocarbon comes into being.

List of Alkanes

  • Methane (CH4)
  • Ethane (C2H6)
  • Propane (C3H8)
  • Butane (C4H10)
  • Pentane (C5H12)
  • Hexane (C6H14)
  • Heptane (C7H16)
  • Octane (C8H18)
  • Nonane (C9H20)
  • Decane (C10H22)

Physical Properties of Alkanes

  • Alkanes are non-polar compounds. The difference in the electronegativities of Carbon and Hydrogen is almost non-existent, hence they have an almost complete absence of polarity.
  • Alkanes generally have relatively lower boiling points and melting points. This is because their atoms have weak Van Der Waals force and so the atomic bonds break easily.
  • However, as the molecules get bigger the force gets stronger. So more complex alkane has higher boiling and melting points.
  • They can exist as solids liquids and gases in their natural states. Unbranched alkanes usually are gases in their natural state. The examples are methane, ethane etc. The alkanes bigger than hexadecane are all solids.
  • Also, they are completely insoluble in water, again due to the weak van der Waal forces.
  • However, they are soluble in organic solids. Here the van der Waal forces of alkane break and are replaced by newer van der Waal forces.

Solved Examples for You

Question: Which of the following alkane(s) do no show isomerism?

  1. Methane
  2. Ethane
  3. Propane
  4. All of the above

Solution: The correct option is “D”. Methane, ethane, and propane do not exhibit any isomerism. The higher alkanes, butane onwards, exhibit chain isomerism.

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