Question

Show (by drawing structures) how the members of a series of alkanes differ from the previous or following member of the series by a \(-\mathrm{CH}_{2}-\) unit.

Short answer

The structure of alkanes can be represented as follows: Methane (CH4): H | H-C-H | H Ethane (C2H6): H H | | H-C-C-H | | H H Propane (C3H8): H H H | | | H-C-C-C-H | | | H H H The change in molecular structure from one alkane to the next involves the addition of a \(-\mathrm{CH}_{2}-\) unit. For example, from methane to ethane and ethane to propane: H H H H H H H H | | | | | | | | H-C-H to H-C-C-H H-C-C-H to H-C-C-C-H | | | | | | | | H H H H H H H H

Step-by-step solution

Draw the structure of the first 3 alkanes

For this exercise, we will draw the structure of the first 3 alkanes: 1. Methane (CH4) 2. Ethane (C2H6) 3. Propane (C3H8) Methane (CH4)$: The structure of methane consists of a single carbon atom surrounded by four hydrogen atoms. In a structural formula, it can be represented as: H | H-C-H | H Ethane (C2H6): The structure of ethane consists of two carbon atoms, each surrounded by three hydrogen atoms. In a structural formula, it can be represented as: H H | | H-C-C-H | | H H Propane (C3H8): The structure of propane consists of three carbon atoms, with the two terminal carbons surrounded by three hydrogen atoms and the middle carbon surrounded by two hydrogen atoms. In a structural formula, it can be represented as: H H H | | | H-C-C-C-H | | | H H H

Compare the structures of adjacent alkanes

Now let's compare the structures of adjacent alkanes and see how they differ from one another. 1. Methane to Ethane: The change in molecular structure from methane to ethane involves the addition of a \(-\mathrm{CH}_{2}-\) unit. H H H | | | H-C-H to H-C-C-H | | | H H H 2. Ethane to Propane: The change in molecular structure from ethane to propane also involves the addition of a \(-\mathrm{CH}_{2}-\) unit. H H H H H | | | | | H-C-C-H to H-C-C-C-H | | | | | H H H H H As we can see, in each case, the change in the structure of an alkane to the next member of the series is due to the addition of a \(-\mathrm{CH}_{2}-\) unit. This pattern will continue for all other alkanes in the series.

Key concepts

methane

Methane is the simplest member of the alkane family. It consists of a single carbon atom bonded to four hydrogen atoms, forming a tetrahedral shape. The chemical formula for methane is \( CH_4 \). This means there are four hydrogen atoms for every carbon atom.

It is a colorless, odorless gas and is the primary component of natural gas. Methane plays a significant role in the energy industry as a fuel source. It is also important in the atmosphere as a greenhouse gas.

Key Characteristics of Methane:

• Molecular formula: \( CH_4 \)
• Structure: One carbon atom bonded to four hydrogen atoms
• Properties: Colorless and odorless gas
• Usage: Primary component of natural gas

Understanding methane is crucial because it serves as the building block for larger, more complex alkanes. When we add a \(-\mathrm{CH}_{2}-\) unit, we get the next member of the alkane series.

ethane

Ethane follows methane in the alkane series and is made up of two carbon atoms and six hydrogen atoms. Its molecular formula is \( C_2H_6 \). Structurally, ethane consists of two carbon atoms connected by a single bond, each of which is surrounded by three hydrogen atoms.

Ethane is commonly used as a feedstock for the production of ethylene, a crucial material for the petrochemical industry. It is a gaseous alkane at room temperature and is colorless and odorless like methane.

Key Features of Ethane:

• Molecular formula: \( C_2H_6 \)
• Structure: Two carbon atoms, six hydrogen atoms
• Properties: Colorless and odorless gas
• Usage: Used in the production of ethylene

The transition from methane to ethane occurs by adding one \(-\mathrm{CH}_{2}-\) unit. This pattern of adding a \( \mathrm{CH}_{2} \) unit continues as we move to the next alkane.

propane

Propane is the third member of the alkane series, comprised of three carbon atoms and eight hydrogen atoms with the chemical formula \( C_3H_8 \). It is a larger molecule than methane and ethane and features a linear chain structure.

In the structure of propane, the central carbon atom is bonded to two other carbon atoms and two hydrogen atoms, while each end carbon atom is bonded to three hydrogen atoms. This configuration makes propane more complex than its predecessors.

Uses and Characteristics of Propane:

• Molecular formula: \( C_3H_8 \)
• Structure: Three carbon atoms in a linear chain
• Properties: Colorless gas, easily liquefied
• Usage: Used as fuel for heating and cooking

The addition of the third \(-\mathrm{CH}_{2}-\) unit transforms ethane into propane, highlighting the consistent growth pattern observed in alkanes. Each step, adding \(-\mathrm{CH}_{2}-\), builds upon the previous structure, creating longer chains.