Single, Double, and Triple Bonds: Understanding Bonding Pairs
Single Bonds: Sharing One Pair of Electrons
Single bond
A single bond occurs when two atoms share one pair of electrons.
- This is the simplest type of covalent bond.
- A single line (—) represents a single bond in a Lewis structure.
- The hydrogen molecule (H₂) forms when two hydrogen atoms each contribute one electron to share a pair.
- This shared pair creates a single bond: $H:H$ or $H—H$
Double Bonds: Sharing Two Pairs of Electrons
Double bond
A double bond forms when two atoms share two pairs of electrons.
- This type of bond is stronger and shorter than a single bond.
- A double line (=) represents a double bond in a Lewis structure.
In an oxygen molecule (O₂), each oxygen atom shares two electrons with the other, forming a double bond: $O::O$ or $O=O$
- When drawing double bonds, students often forget that each atom must still satisfy the octet rule (or duet rule for hydrogen).
- For example, in O₂, each oxygen atom has four non-bonding electrons in addition to the shared pairs.
Triple Bonds: Sharing Three Pairs of Electrons
Triple bond
A triple bond occurs when two atoms share three pairs of electrons.
- This bond is the strongest and shortest of the three types.
- A triple line (≡) represents a triple bond in a Lewis structure.
In a nitrogen molecule (N₂), each nitrogen atom shares three electrons with the other, forming a triple bond: $N:::N$ or $N≡N$
Bond Length and Bond Strength
Now that you understand the types of bonds, let’s explore how they differ in terms of bond length and bond strength.
Bond Length: How Far Apart Are the Atoms?
Bond length
Bond length is the average distance between the nuclei of two bonded atoms.
- As the number of shared electron pairs increases, the bond length decreases.
- This is because more shared electrons create a stronger attraction between the nuclei, pulling the atoms closer together.
Single bonds > Double bonds > Triple bonds (in terms of length)
Bond Strength: How Much Energy is Needed to Break the Bond?
Bond strength
Bond strength refers to the energy required to break a bond.
- As the number of shared electron pairs increases, the bond strength increases.
- More shared electrons mean a stronger electrostatic attraction between the atoms.
Triple bonds > Double bonds > Single bonds (in terms of strength)
Remember that shorter bonds are stronger because the nuclei are held more tightly together by the shared electrons.
- What is the relationship between bond length and bond strength?
- How does the number of bonding pairs affect molecular stability?
- Why are triple bonds shorter and stronger than single bonds?
