What are the molecular and structural formulas for alkenes when n=2 and n=3?

Alkenes are hydrocarbons with at least one carbon-carbon double bond. Their general molecular formula is $\text{C}_n\text{H}_{2n}$, where $n$ represents the number of carbon atoms.

For $n=2$, substitute into the general formula:

This compound is called ethene.

The structural formula for ethene shows two carbon atoms connected by a double bond, with each carbon atom also bonded to two hydrogen atoms:

For $n=3$, substitute into the general formula:

This compound is called propene.

The structural formula for propene shows a three-carbon chain with a double bond between the first two carbon atoms:

Or more compactly: $\text{CH}_2=\text{CH}-\text{CH}_3$.

Here are the completed formulas:

• For $n=2$:
  • Molecular Formula: $\boxed{\text{C}_2\text{H}_4}$
  • Structural Formula: $\boxed{\text{H}_2\text{C}=\text{CH}_2}$
• For $n=3$:
  • Molecular Formula: $\boxed{\text{C}_3\text{H}_6}$
  • Structural Formula: $\boxed{\text{CH}_2=\text{CH}-\text{CH}_3}$