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Structural Formula: Definition & Examples

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  • 0:00 What is a Structural Formula?
  • 0:59 Structural Formulas:…
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Lesson Transcript
Instructor: Nissa Garcia

Nissa has a masters degree in chemistry and has taught high school science and college level chemistry.

Chemical compounds are made of atoms bonded together. The way the atoms are bonded together in a compound is shown by its structural formula. In this lesson, we will learn about the different types of structural formulas and look at an example for each formula.

What Is a Structural Formula?

We have chemical compounds all around us - they are in our food, drinks and in objects we use every single day. These chemical compounds can be identified by their molecular formulas. A few examples are shown in the following illustration:

Examples of common compounds and their molecular formulas

While the molecular formula shows what how many atoms there are for each element present in the compound, it does not tell us about how the elements are bonded together. We don't know which atom of an element is bonded to which. This is where the structural formula comes in.

The structural formula shows how the atoms are arranged and bonded together in a molecular formula of a chemical compound. Let's take a look at the compounds vinegar and ethyl alcohol, and compare their molecular formulas with their structural formulas:

Structural formulas of acetic acid and ethyl alcohol

Without the structural formula, we wouldn't know that acetic acid has a carbon atom double-bonded together with oxygen. By looking at the structural formula, we can see the spatial arrangement of the atoms in the compound.

Structural Formula: Types and Examples

It is always good to have choices, and the same goes with how we draw structural formulas. There are different ways to represent a compound's structural formula. The earlier examples illustrate just one way of drawing the structural formula. In this upcoming section, we'll look at the different types of structural formulas.

The electron dot structural formula representation uses dots to represent the electrons involved with the bonding between different atoms. Let's take a look at the following compounds: water, ammonia and ethanol. Here, you can see the nonbonding electrons in red and the bonding electrons between the atoms in black:

Examples of the electron dot structural formula

Line-bond structural formula: The line-bond structural formula is a very commonly used representation of the structural formula. Like the name suggests, the line-bond structural formula uses lines and bonds to show the covalent bonds between atoms. This gives us a simpler and less cluttered representation of the structural formula. Instead of drawing dots between atoms, we draw lines. One line is equivalent to one pair of bonding electrons. The red dots are the nonbonding electrons. Here are the line-bond structural formula versions of the same compounds shown in the electron dot formula representation:

Examples of the line-bond structural formula

For organic compounds (carbon containing compounds) like ethanol, we usually don't show the nonbonding electrons, the red dots. We can omit the nonbonding electrons, the red dots, for organic compounds.

Condensed structural formula: The condensed structural formula still uses lines between bonded atoms, but is an easier and shorter way to draw the line-bond structural formula because it omits the carbon and hydrogen bonds. We can see this when we compare the line-bond structural formula with the condensed structural formula.

Comparison between the line-bond structural formula and condensed structural formula

Skeletal structural formula: The skeletal structural formula is a variation of the structural formula where the hydrogen atoms are not shown, but the carbon atoms are represented by the edges of the chain or line. We can see this here in the comparison of the condensed structural formula with the skeletal structural formula:

Comparison between the condensed structural formula and skeletal structural formula

This way of writing the structural formula makes it even more convenient and easier, especially when you want to draw bigger and more complex molecules.

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