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4.3: Single Covalent Bonds

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      Democritus believed atoms were held together by hooks
    Figure \(\PageIndex{1}\) (Credit: Courtesy of the ​​​​​​​US Department of the Interior; Source: Commons Wikimedia, Fishhook(opens in new window) []; License: Public Domain)

    What holds molecules together?

    In one form or another, the idea of atoms connecting to form larger substances has been with us for a long time. The Greek philosopher Democritus (460-370 BCE) believed that atoms had hooks that allowed them to connect with one another. Today, we believe that atoms are held together by bonds formed when two atoms share a set of electrons—a much more complicated picture than the simple hooks that Democritus believed in.

    Single Covalent Bonds

    A covalent bond forms when two orbitals with one electron each overlap one another. For the hydrogen molecule, this can be shown as:

    Electronic configuration of a hydrogen molecule
    Figure \(\PageIndex{2}\) (Credit: Joy Sheng; Source: CK-12 Foundation; License:  CC  BY-NC 3.0(opens in new window))

    Upon formation of the \(\ce{H_2}\) molecule, the shared electrons must have opposite spin, so they are shown with opposite spin in the atomic \(1s\) orbital.

    The halogens also form single covalent bonds in their diatomic molecules. An atom of any halogen, such as fluorine, has seven valence electrons. Its unpaired electron is located in the \(2p\) orbital.

    CK12 Screenshot 9-3-2.png
    Figure \(\PageIndex{3}\) (Credit: Joy Sheng; Source: CK-12 Foundation; License: CC BY-NC 3.0(opens in new window))

    The single electrons in the third \(2p\) orbital combine to form the covalent bond:

    Figure \(\PageIndex{4}\): On the left is a fluorine atom with seven valence electrons. On the right is the \(\ce{F_2}\) molecule. (Credit: Jodi So; Source: CK-12 Foundation; License: CC BY-NC 3.0(opens in new window))

    The diatomic fluorine molecule \(\left( \ce{F_2} \right)\) contains a single shared pair of electrons. Each \(\ce{F}\) atom also has three pair of electrons that are not shared with the other atom. A lone pair is a pair of electrons in a Lewis electron-dot structure that is not shared between atoms. The oxygen atom in the water molecule shown below has two lone pair sets of electrons. Each \(\ce{F}\) atom has three lone pairs. Combined with the two electrons in the covalent bond, each \(\ce{F}\) atom follows the octet rule.

    Example \(\PageIndex{1}\)

    Draw the Lewis electron dot structure for water.

    Step 1: List the known quantities and plan the problem.
    • Molecular formula of water \(= \ce{H_2O}\)
    • \(1 \: \ce{O}\) atom \(= 6\) valence electrons
    • \(2 \: \ce{H}\) atoms \(=2 \times 1 = 2\) valence electrons
    • Total number of valence electrons \(=8\)

    Use the periodic table to determine the number of valence electrons for each atom and the total number of valence electrons. Arrange the atoms and distribute the electrons so that each atom follows the octet rule. The oxygen atom will have 8 electrons, while the hydrogen atoms will each have 2.

    Step 2: Solve.

    Electron dot diagrams for each atom are:

    Lewis electron dot diagrams for hydrogen and oxygen
    Figure \(\PageIndex{5}\) (Credit: Joy Sheng; Source: CK-12 Foundation; License: CC BY-NC 3.0(opens in new window))

    Each hydrogen atom with its single electron will form a covalent bond with the oxygen atom where it has a single electron. The resulting Lewis electron dot structure is:

    Lewis electron dot structure of water
    Figure \(\PageIndex{6}\) (Credit: Joy Sheng; Source: CK-12 Foundation; License: CC BY-NC 3.0(opens in new window))
    Step 3: Think about your result.

    The oxygen atom follows the octet rule with two pairs of bonding electrons and two lone pairs. Each hydrogen atom follows the octet rule with one bonding pair of electrons.


    • Covalent bonds form when electrons in two atoms form overlapping orbitals.
    • Lone pair electrons in an atom are not shared with any other atom.


    1. How does a covalent bond form?
    2. What relationship do the spins of shared electrons have with each other?
    3. Do lone pair electrons form covalent bonds?

    4.3: Single Covalent Bonds is shared under a CC BY-NC license and was authored, remixed, and/or curated by LibreTexts.