Question

Write the general formula for a normal alkane. How does a given alkane differ from the previous or the following member of the series?

Short answer

The general formula for normal alkanes is \(C_nH_{2n+2}\), where 'n' is the number of carbon atoms in the alkane. Consecutive members of the alkane series differ by one carbon atom (C) and two hydrogen atoms (H2) - as we move from one member to the next, the number of carbon atoms increases by one and the number of hydrogen atoms increases by two.

Step-by-step solution

General formula for normal alkanes

The general formula for normal alkanes is CnH2n+2, where 'n' is the number of carbon atoms in the alkane.

Differences between consecutive members

Consecutive members of the alkane series differ by one carbon atom (C) and two hydrogen atoms (H2). When we move from one member to the next, the number of carbon atoms increases by one and the number of hydrogen atoms increases by two.

Key concepts

Hydrocarbons

Hydrocarbons are organic compounds composed entirely of carbon and hydrogen atoms. These molecules are the simplest form of organic chemistry and serve as a fundamental building block for more complex molecules. Alkanes, a type of hydrocarbon, are saturated, meaning they have only single bonds between the carbon atoms. This saturation gives alkanes their characteristic stability and makes them less reactive compared to other hydrocarbons like alkenes or alkynes that contain double or triple bonds, respectively.
Hydrocarbons are primarily found in fossil fuels such as coal, petroleum, and natural gas. These compounds release energy when combusted, which makes them a valuable resource for energy production.

Molecular Formula

The molecular formula is a concise way to express the types and numbers of atoms in a molecule. For alkanes, the molecular formula follows a specific pattern: CnH2n+2. This indicates that an alkane molecule with 'n' carbon atoms will have \(2n+2\) hydrogen atoms.
This formula helps us understand the structural composition of alkanes and predict the makeup of each member in the alkane series. It provides a straightforward representation, showing the proportional relationship between carbon and hydrogen atoms within normal alkanes.

Carbon Atoms

Carbon atoms form the backbone of hydrocarbon structures, including alkanes. Every carbon atom is capable of forming four covalent bonds, allowing them to link together in chains of varying lengths. In alkanes, each carbon atom is bonded to hydrogen atoms in such a way that satisfies its tetravalency, the state of having four chemical bonds.
In the context of alkanes, each additional carbon atom typically increases the chain length, affecting properties such as melting and boiling points. The increase by one carbon atom in consecutive alkanes results in a distinct difference in physical properties as the chain becomes longer.

Hydrogen Atoms

In alkanes, hydrogen atoms are bonded to carbon in a specific ratio as described by the formula CnH2n+2. Hydrogen atoms fulfill the remaining valencies of carbon atoms, thus ensuring that all carbon atoms achieve complete saturation with single bonds.
The presence of two additional hydrogen atoms for each additional carbon atom is a unique feature of alkanes. This constant addition maintains a balance in the molecular structure, ensuring stability and a distinct stepwise change in the molecular formula as we move through the homologous series of alkanes.
Hydrogen atoms also play a significant role in determining the geometry and overall structure of alkanes, which in turn influences their chemical properties and behavior in reactions.