Question Video: Determining the Structural Formula of an Alkane from an Alkane Name | Nagwa Question Video: Determining the Structural Formula of an Alkane from an Alkane Name | Nagwa

Question Video: Determining the Structural Formula of an Alkane from an Alkane Name Chemistry • Third Year of Secondary School

What is the structural formula of propane?

02:50

Video Transcript

What is the structural formula of propane?

In this question, we are being asked to determine the structural formula of a propane molecule. A structural formula is a text representation of the bonding in a molecule that lists atoms in the order in which they are connected. There are several other ways to represent the composition and structure of a molecule. For example, a displayed formula shows all the atoms and bonds in a molecule. And the bonds are drawn as lines.

It can be very helpful to draw a displayed formula of a molecule before trying to compose the structural formula. Let’s get started by examining the name propane. In the name, the prefix prop- indicates that there are a total of three carbon atoms present in the molecule, while the ending A-N-E tells us that the molecule is a type of hydrocarbon called an alkane. In an alkane, there are only single bonds between the carbon atoms. Let’s go ahead and use the information we gathered from the name to sketch out a displayed formula for propane.

We can start by connecting three carbon atoms with single bonds. The remaining atoms in the molecule are hydrogen atoms. And each carbon atom can only have a total of four single bonds. In our drawing, the first carbon atom currently has only one bond. So this carbon atom can have three single bonds to hydrogen atoms. The second carbon atom currently has two single bonds. So this carbon atom can have two single bonds to hydrogen atoms. Finally, the third carbon atom currently has only one single bond. Therefore, this carbon atom can have three single bonds with hydrogen atoms.

Now, we’re ready to write the structural formula of propane. We can start by breaking the displayed formula into separate units. Each unit is composed of a carbon atom and the hydrogen atoms to which it is bonded. The first carbon atom in the propane molecule is bonded to three hydrogen atoms. Therefore, we can write this unit as CH3, where the subscript three represents the number of hydrogen atoms to which the carbon atom is bonded. The second carbon atom in the propane molecule is bonded to two hydrogen atoms. We can write this unit as CH2. Finally, the third carbon atom in the propane molecule is bonded to three hydrogen atoms. Therefore, we can write this unit as CH3. In conclusion, the structural formula of propane is CH3CH2CH3.

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