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Lewis Structures: Single, Double & Triple Bonds

  • 0:08 Lewis Dot Structures…
  • 1:18 Structural Formula
  • 2:10 Examples
  • 4:17 Lesson Summary
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Lesson Transcript
Instructor: Amy Meyers

Amy holds a Master of Science. She has taught science at the high school and college levels.

Review what a Lewis dot diagram is and discover how to draw a Lewis dot structural formula for compounds. Learn how to represent single, double and triple bonds with lines instead of dots. Also learn how compounds arrange themselves.

Lewis Dot Structure for Compounds

Lewis dot structures, as you have learned, are a way to diagram an element and easily show its valence electrons. A Lewis dot structure is a diagram that shows the valence electrons in an element. In a Lewis structure, the nucleus of the element is represented by its symbol. The valence electrons are represented by dots placed around the symbol in pairs. In this way, you can easily see when an element's valence shell isn't completely filled.

A Lewis dot structure represents an element or compound and its valence electrons
Lewis Dot Structure

You can also write Lewis dot structures for compounds. For example, you know that nitrogen has five valence electrons, is represented by N and wants to fill its outer shell with eight total electrons. If nitrogen were to bond with another nitrogen, the Lewis dot structure would look like this. You can see that nitrogen shares three pairs of electrons. Scientists get a bit lazy and don't want to make all those dots, so instead, they write a line between the two symbols, so it looks like this - (N-N). They leave off the extra dots. They assume them to be there; they're just too lazy to write them. Just remember that hydrogen is the exception to the rule and only likes two electrons in its outer shell.

Structural Formula

A structural formula is a way of showing the location of the atoms or ions relative to one another in a molecule while also showing the number and location of the bonds between them. This can tell you many things about a compound. It tells you what kind of atoms are involved, the number of them, how they are arranged and the bonds between atoms.

The steps to writing Lewis dot structures for compounds are simple.

  1. Determine the type and number of atoms in the molecule.
  2. Write the Lewis dot structure for each individual atom.
  3. Connect the atoms by electron pair bonds so that each atom has a full octet. If you have carbon in your molecule, it is always in the middle. Hydrogens are usually on the outside.
  4. Double-check your work and make sure every atom has eight electrons and no more.

Examples

Let's start with an easy one: hydrogen, H2. Each hydrogen atom has one valence electron. Individually, they look like this. When they form a compound, they look like this - (H:H). This structure represents a stable hydrogen molecule where both atoms are sharing the pair of electrons.

An example of what the Lewis dot structure looks like in H2
Lewis Dots in H2

Try a slightly harder one. Chlorine has seven valence electrons. It looks like this. It likes to form bonds with itself. Cl2 looks like this - (Cl:Cl). It can also be represented with a line between the two atoms, like this - (Cl-Cl). Often, scientists get lazy, drop the extra dots and just put the line for the bond.

Sometimes atoms share more than one electron and form more than one pair, such as in O2. In this case, you put four dots between the two letters, or two lines to signify two bonds or two pairs of shared electrons. The same would go for three or four pairs. Four pairs, or bonds, are the most any two atoms can share.

Try doing CH2O:

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