Understanding the Chemical Formula of Propene

To determine the chemical formula of propene, we first need to identify the type of hydrocarbon it is and the number of carbon atoms it contains.

Identifying Propene as an Alkene

The name 'propene' ends with the suffix '-ene'. This suffix indicates that the molecule is an alkene. Alkenes are a class of hydrocarbons that contain at least one carbon-carbon double bond ($\text{C}=\text{C}$).

General Formula for Alkenes

Alkenes that have only one double bond and are not cyclic follow a general chemical formula. This formula relates the number of carbon atoms ($\text{n}$) to the number of hydrogen atoms.

The general formula for straight-chain or branched alkenes with one double bond is $\text{C}_{\text{n}}\text{H}_{2\text{n}}$, where $\text{n}$ represents the number of carbon atoms.

Determining the Number of Carbon Atoms in Propene

The prefix 'prop-' in organic chemistry names signifies a chain of three carbon atoms. So, for propene, the number of carbon atoms ($\text{n}$) is 3.

Calculating the Chemical Formula of Propene

Now we can substitute the value of $\text{n} = 3$ into the general formula for alkenes, $\text{C}_{\text{n}}\text{H}_{2\text{n}}$:

Number of carbon atoms ($\text{n}$) = 3

Number of hydrogen atoms = $2 \times \text{n} = 2 \times 3 = 6$

Therefore, the chemical formula for propene is $\text{C}_3\text{H}_6$.

Comparing with Options

Let's compare our calculated formula with the given options:

• Option 1: $\text{C}_2\text{H}_4$ (This is Ethene, $\text{n}=2$)
• Option 2: $\text{C}_3\text{H}_4$ (This formula fits an alkyne with 3 carbons, Propyne)
• Option 3: $\text{C}_3\text{H}_6$ (This matches our calculation for Propene)
• Option 4: $\text{C}_2\text{H}_2$ (This is Ethyne, $\text{n}=2$, an alkyne)

The calculated formula $\text{C}_3\text{H}_6$ matches Option 3.

Conclusion on Propene's Formula

Based on the rules of organic nomenclature and the general formula for alkenes, the chemical formula for propene (with three carbon atoms and one double bond) is $\text{C}_3\text{H}_6$.

Revision Table: Hydrocarbon Series

Additional Information on Alkenes and Propene

• Alkenes are unsaturated hydrocarbons because they contain a double bond, meaning they could theoretically hold more hydrogen atoms if the double bond were broken.
• The simplest alkene is ethene ($\text{C}_2\text{H}_4$), also commonly known as ethylene. The 'meth-' prefix (for one carbon) is not used for alkenes or alkynes because a double or triple bond requires at least two carbon atoms.
• Propene ($\text{C}_3\text{H}_6$) is an important industrial chemical used in the production of plastics like polypropylene.
• The position of the double bond matters for alkenes with four or more carbon atoms, leading to isomers (molecules with the same chemical formula but different structures), but for propene ($\text{C}_3\text{H}_6$), there is only one possible structure.