Multiple Bonds (Simplified): Videos & Practice Problems

To accurately draw a Lewis structure, understanding the necessity of multiple bonds is crucial. Single bonds are the longest, while triple bonds are the shortest, with bond length decreasing as bond order increases. Each covalent bond involves two electrons: a single bond shares 2 electrons (1 pair), a double bond shares 4 electrons (2 pairs), and a triple bond shares 6 electrons (3 pairs). This knowledge is essential for grasping concepts like valence electrons and molecular geometry, which are foundational in organic chemistry.

Multiple Bonds (Simplified) Concept 1

We're going to say in order to draw a correct Lewis structure, multiple bonds between elements are sometimes necessary. So here we have a single bond, a double bond, and a triple bond. What we need to realize here first in terms of their bond length is notice that as we go from a single bond to a triple bond, the bond length is decreasing. Single bonds are the longest, triple bonds are the shortest. In addition to this, realize that every time we make a covalent bond it involves 2 electrons. So there's an electron here at this end and here at this end. This tells us the number of valence electrons that are shared between the 2 atoms. Here in a single bond, there are 2 valence electrons that are being shared between the 2 carbons, this equals 1 electron pair. In a double bond, we have 2 bonds. Each one again has 2 electrons, so that's a total of 4 valence electrons or 2 electron pairs. And then finally, a triple bond has 3 bonds. Each one has 2 electrons. So that's a total of 6 valence electrons shared, which equates to 3 electron pairs.

Multiple Bonds (Simplified) Example 1

Here it says identify how many single, double, and triple bonds are in the following molecule of C₃H₃N. Alright. So let's look at single bonds first. So here we have 1, 2, 3, 4 single bonds. For double bonds, we have 1 double bond. And then finally, triple bonds. We have 1 triple bond within this structure. So that would equal the number of single bonds, double bonds, and triple bonds that we can find within the molecule of C₃H₃N.

Complete following structures by filling in with lone pairs and double or triple bonds.

• A.
• B.
• C.
• D.

Answer: (D)

Here’s what students ask on this topic:

What is the difference between single, double, and triple bonds in terms of bond length and electron pairs?

Single, double, and triple bonds differ in both bond length and the number of electron pairs shared. A single bond is the longest and involves one pair of electrons (2 electrons). A double bond is shorter than a single bond and involves two pairs of electrons (4 electrons). A triple bond is the shortest and involves three pairs of electrons (6 electrons). As the number of shared electron pairs increases, the bond length decreases.

How do you determine the number of valence electrons shared in a multiple bond?

To determine the number of valence electrons shared in a multiple bond, count the number of bonds between the atoms and multiply by 2 (since each bond involves 2 electrons). For example, a single bond shares 2 electrons, a double bond shares 4 electrons, and a triple bond shares 6 electrons. This helps in understanding the electron distribution in the molecule.

Why are triple bonds shorter than single bonds?

Triple bonds are shorter than single bonds because they involve more shared electron pairs, which increases the electrostatic attraction between the bonded atoms. This stronger attraction pulls the atoms closer together, resulting in a shorter bond length. In contrast, single bonds have fewer shared electrons and thus a weaker attraction, leading to a longer bond length.

How does the bond order affect the bond strength and bond length?

Bond order, which is the number of shared electron pairs between two atoms, directly affects both bond strength and bond length. Higher bond orders (e.g., double and triple bonds) result in stronger bonds due to increased electron sharing, and shorter bond lengths due to the stronger attraction between the atoms. Conversely, lower bond orders (e.g., single bonds) result in weaker bonds and longer bond lengths.

What role do multiple bonds play in determining molecular geometry?

Multiple bonds significantly influence molecular geometry by affecting bond angles and the overall shape of the molecule. Double and triple bonds create regions of higher electron density, which can repel other electron pairs more strongly, altering bond angles. For example, in ethene (C₂H₄), the double bond between carbon atoms creates a planar structure with bond angles of approximately 120°. Understanding these effects is crucial for predicting and explaining molecular shapes.