Problem 24 - Chemistry An Atoms First Approach

Question

Draw the structures for two examples of unsaturated hydrocarbons. What structural feature makes a hydrocarbon unsaturated?

Step-by-Step Solution

Answer

Two examples of unsaturated hydrocarbons are ethene and ethyne. Ethene has the molecular formula \( C_{2}H_{4} \) and its structure is: H H \ / C=C / \ H H Ethyne has the molecular formula \( C_{2}H_{2} \) and its structure is: H H \ / C≡C / \ H H The structural feature that makes a hydrocarbon unsaturated is the presence of double or triple bonds between the carbon atoms. Ethene has a double bond, and ethyne has a triple bond between carbon atoms, making them both unsaturated hydrocarbons.

Step 1: Understanding Saturated and Unsaturated Hydrocarbons

A hydrocarbon is an organic compound that consists of hydrogen (H) and carbon (C) atoms. These compounds can be classified into two main groups based on the type of chemical bonds between the carbon atoms: saturated and unsaturated hydrocarbons. Saturated hydrocarbons have single bonds between the carbon atoms, while unsaturated hydrocarbons have one or more double or triple bonds between the carbon atoms.

Step 2: Knowing the General Formulas for Alkenes and Alkynes

Unsaturated hydrocarbons can be further divided into two categories: alkenes and alkynes. Alkenes have one or more carbon-carbon double bonds denoted by the general formula \( C_{n}H_{2n} \), whereas alkynes have one or more carbon-carbon triple bonds denoted by the general formula \( C_{n}H_{2n-2} \).

Step 3: Drawing Examples of Alkenes and Alkynes

Let's draw the structures of one alkene and one alkyne, which are both unsaturated hydrocarbons. Example 1: Ethene (an alkene) Ethene has two carbon atoms and falls under the alkene category, so its molecular formula will be \( C_{2}H_{4} \). The structure of ethene is drawn as follows: H H \ / C=C / \ H H Example 2: Ethyne (an alkyne) Ethyne has two carbon atoms and falls under the alkyne category, so its molecular formula will be \( C_{2}H_{2} \). The structure of ethyne is drawn as follows: H H \ / C≡C / \ H H

Step 4: Identifying the Structural Feature that Makes a Hydrocarbon Unsaturated

The structural feature that makes hydrocarbons unsaturated is the presence of double or triple bonds between the carbon atoms. In the examples, ethene has a double bond and ethyne has a triple bond between carbon atoms, making them both unsaturated hydrocarbons.