5.3Covalent Bond
Covalent bonds are formed when non-metal atoms share their electrons to achieve a stable duplet or octet electron arrangement. Depending on the number of electron pairs shared between atoms, covalent bonds are categorised into single bonds, double bonds, and triple bonds. Understanding how non-metal atoms interact through covalent bonding provides insight into molecular structures and how they differ from ionic compounds.
Learning Objectives
- Explain with examples the formation of covalent bonds (single bond, double bond, and triple bond).
- Visualise the formation of covalent bonds using electron arrangement diagrams and Lewis structures.
- Compare ionic bonds and covalent bonds in terms of their formation, particles involved, and characteristics.
Covalent Bond Formation
Non-metal atoms share valence electrons to form single, double and triple bonds.
Single Bond
Two atoms share one pair of electrons (2 electrons).
Example: Chlorine molecule, Cl2
Each chlorine atom has electron arrangement 2.8.7 and needs 1 electron to achieve a stable octet. The shared pair gives each chlorine atom the arrangement 2.8.8.
Double Bond
Two atoms share two pairs of electrons (4 electrons).
Example: Oxygen molecule, O2
Each oxygen atom has electron arrangement 2.6 and needs 2 electrons. The two shared pairs give each oxygen atom the arrangement 2.8.
Triple Bond
Two atoms share three pairs of electrons (6 electrons).
Example: Nitrogen molecule, N2
Each nitrogen atom has electron arrangement 2.5 and needs 3 electrons. The three shared pairs give each nitrogen atom the arrangement 2.8.
Lewis Structure
Shows only the valence electrons of the atoms involved.
A shared pair is represented by a line: Cl–Cl, O=O, N≡N.
Brief Explanation
Understand how covalent bonds form and how they are represented.
Single Bond
Formed when two atoms share one pair of electrons (1 pair = 2 electrons).
Example: Cl2. Two chlorine atoms each contribute one electron to share a pair of electrons, forming a single bond.
Double Bond
Formed when two atoms share two pairs of electrons (2 pairs = 4 electrons).
Example: O2. Two oxygen atoms each contribute two electrons to share two pairs of electrons, forming a double bond.
Triple Bond
Formed when two atoms share three pairs of electrons (3 pairs = 6 electrons).
Example: N2. Two nitrogen atoms each contribute three electrons to share three pairs of electrons, forming a triple bond.
Lewis Structure
Visualises covalent bond formation by showing only the valence electrons of the atoms involved.
A pair of shared electrons is represented with a line between the two atoms: Cl–Cl, O=O, N≡N.
Electron Arrangement Diagrams and Lewis Structures
In electron arrangement diagrams, valence electrons from different atoms are shown as dots and crosses. In Lewis structures, each line represents one shared pair of electrons, while lone pairs are shown as pairs of dots.
| Molecule | Electron arrangement diagram | Lewis structure with lone pairs |
|---|---|---|
| Cl2 | :Cl• ×Cl: with 3 lone pairs on each Cl atom | .. ..
:Cl–Cl:
.. .. |
| O2 | O•• ××O with 2 lone pairs on each O atom | .. ..
O=O
.. .. |
| N2 | N••• ×××N with 1 lone pair on each N atom | :N≡N: |
| Bond type | Shared electron pairs | Shared electrons | Example |
|---|---|---|---|
| Single bond | 1 pair | 2 electrons | Cl2 |
| Double bond | 2 pairs | 4 electrons | O2 |
| Triple bond | 3 pairs | 6 electrons | N2 |
Comparison between Ionic Bond and Covalent Bond
Similarities and differences in formation, particles involved and participating elements.
Similarities
- Involve valence electrons only.
- Atoms achieve a stable octet or duplet electron arrangement.
Ionic Bond
- Formed between metal atoms and non-metal atoms.
- Involves the transfer of electrons.
- Forms a positively-charged ion and a negatively-charged ion.
Covalent Bond
- Formed between non-metal atoms.
- Involves the sharing of electrons.
- Forms molecules.
Chemistry Lens: Diamond
Diamond is one of the hardest substances in the world due to the formation of covalent bonds between carbon atoms.
Each carbon atom, C, forms four covalent bonds with another four carbon atoms.
Try These Questions First
Answer mentally, then check the explanation.
How many pairs of electrons are shared between two nitrogen atoms in a nitrogen molecule, N2?
What type of bond is formed when an oxygen atom combines with another oxygen atom?
State one similarity between an ionic bond and a covalent bond.
Common Mistakes
Avoid these errors when describing covalent bonds.
Common Misconceptions
Compare each misconception with the correct fact.
Covalent bonds involve the transfer of electrons from one non-metal to another.
Covalent bonds strictly involve the sharing of electrons between non-metal atoms; no transfer occurs.
A single line in a Lewis structure represents a single electron.
A single line in a Lewis structure represents one shared pair of electrons (two electrons).
Covalent bonding always results in charged particles.
Covalent bonding produces neutral molecules, whereas ionic bonding produces positively and negatively charged ions.
Summary
Key facts to remember.
- Covalent bonds form between non-metal atoms through the sharing of valence electrons to attain stable duplet or octet arrangements.
- Single bond = 1 shared pair of electrons (e.g., Cl2).
- Double bond = 2 shared pairs of electrons (e.g., O2).
- Triple bond = 3 shared pairs of electrons (e.g., N2).
- Lewis structures illustrate valence electrons and represent shared pairs as lines.
- Both ionic and covalent bonds involve valence electrons to achieve stability, but ionic bonding involves electron transfer between metals and non-metals forming ions, while covalent bonding involves electron sharing between non-metals forming molecules.
Quick Activity
Complete all parts before checking your score.
A. Objective Quiz
Which molecule contains a triple covalent bond formed by sharing three pairs of electrons?
Which of the following is a characteristic of covalent bond formation?
B. Fill in the Blanks
A double bond is formed when two atoms share ______ pairs of electrons.
In a Lewis structure, a pair of electrons shared between two atoms is represented with a ______ between the two atoms.
C. Match the Description to the Type of Chemical Bond
Drag each description on desktop. On mobile, tap a description and then tap the matching box.
Descriptions
Formed between metal atoms and non-metal atoms Involves the sharing of electrons Forms positively-charged and negatively-charged ions Forms neutral moleculesTypes of Bond
Keywords
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