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.
