Atomic Foundations of Matter · Lesson 5 of 14
Bonding by Sharing of Electrons — Covalent Bond
“Hydrogen, chlorine and oxygen show how one or more shared electron pairs can hold atoms together.”
• Define a covalent bond. • Explain formation of hydrogen and chlorine molecules. • Distinguish a single bond from a double bond. • Explain formation of an oxygen molecule. • Use valence electrons to reason about nitrogen and fluorine molecules.
Imagine two atoms that each need additional electrons to complete a stable outer shell. Instead of one atom permanently giving an electron to the other, the atoms can share electrons. The shared electrons are attracted by both nuclei, helping hold the atoms together.
Bonding by Sharing of Electrons — Covalent Bond
A chemical bond formed through the sharing of electron pairs between atoms.
Molecules of Elements
Formation of a Hydrogen Molecule
A hydrogen atom has atomic number 1, so a neutral hydrogen atom has one electron. That electron occupies the K shell, which can accommodate two electrons. Two hydrogen atoms can each contribute one electron to a shared pair. In this arrangement, each hydrogen has access to two electrons around the bonding region and reaches a stable duplet.
When one pair of electrons is shared between two atoms, the atoms are joined by a single covalent bond. The bond can be represented by a single line.
Formation of a Chlorine Molecule
A chlorine atom has seven valence electrons. It requires one more electron to complete an octet. Two chlorine atoms can each contribute one electron to a shared pair. Each chlorine then has access to the shared pair and reaches a stable outer-shell arrangement.
Formation of an Oxygen Molecule
An oxygen atom has six valence electrons and requires two more to complete an octet. Two oxygen atoms therefore share two electrons each, producing two shared pairs between them. A bond involving two shared electron pairs is called a double bond.
Using Valence Electrons to Predict Sharing
Nitrogen has five valence electrons, so each nitrogen atom needs access to three additional electrons to complete an octet. The chapter asks you to draw the structure of the nitrogen molecule using this electron-sharing idea. Fluorine has seven valence electrons, so two fluorine atoms can each share one electron to form a molecule with a single shared pair.
Problem
The atomic number of fluorine is 9. Explain how a fluorine molecule forms.
- 1.A neutral fluorine atom has 9 electrons, distributed as 2, 7.
- 2.It has seven valence electrons and needs one additional electron to complete an octet.
- 3.A second fluorine atom has the same requirement.
- 4.Each fluorine contributes one electron to one shared pair.
- 5.Both atoms then reach stable outer-shell arrangements, forming a single covalent bond in F₂.
The chapter uses electron sharing as an analogy for cooperation: sharing can create a stable whole from separate participants. In chemistry, however, the stability is explained by electron arrangement and attraction between shared electrons and nuclei.
Quiz
Which description best matches Covalent Bond?
Which term matches this description: A chemical bond formed through the sharing of electron pairs between atoms.
Which statement is a key takeaway from this lesson?
Which additional statement is also a key takeaway from this lesson?
Which further statement is also a key takeaway from this lesson?
Practice Problems
- Explain why H₂ has a single covalent bond.
- Explain why O₂ requires a double bond in the model used here.
- Use five valence electrons to reason about how two nitrogen atoms can complete their octets.
- Use fluorine's electronic configuration to explain F₂ formation.
- Distinguish a shared electron pair from a double bond.
Key Takeaways
• A covalent bond forms when atoms share one or more pairs of electrons. • Sharing allows atoms to achieve more stable outer electron arrangements. • A single bond contains one shared electron pair, while multiple bonds contain more than one shared pair. • Hydrogen, chlorine and oxygen illustrate different patterns of covalent bonding.