2.1.4 Covalent Bonding

In this lesson, we will explore the formation of covalent bonds when atoms share pairs of electrons. We will discuss the strength of these bonds and how covalently bonded substances can exist as small molecules, polymers, or giant covalent structures.

Covalent Bonds and Electron Sharing

Covalent bonding occurs when atoms share pairs of electrons to achieve a stable electron configuration. These bonds between atoms are strong due to the sharing of electrons, resulting in a stable arrangement of atoms.

Small Molecules

Many covalently bonded substances exist as small molecules. These substances consist of a few atoms bonded together by covalent bonds. Examples include water (H₂O), carbon dioxide (CO₂), and methane (CH₄). These molecules are typically held together by relatively weak intermolecular forces.

Polymers

Some covalently bonded substances have very large molecules known as polymers. Polymers are formed when many small molecules, called monomers, are chemically bonded together. Examples of polymers include polyethylene, polypropylene, and polyvinyl chloride (PVC). These substances have unique properties due to their long-chain structure.

Giant Covalent Structures

Certain covalently bonded substances have giant covalent structures, meaning they consist of a vast number of atoms bonded together by strong covalent bonds. Diamond and silicon dioxide (SiO₂) are examples of giant covalent structures. In these structures, each atom is bonded to multiple neighbouring atoms, resulting in a rigid and stable latticeHighly organised structure of repeating atoms/molecules that forms a crystalline structure..

Representing Covalent Bonds

Covalent bonds in small molecules can be represented using a line to represent a single bond between two atoms. For example, in the molecule H₂O, the oxygen atom is bonded to two hydrogen atoms, and this can be represented as H-O-H. In polymers, the repeating units can be represented with lines between atoms, indicating the covalent bonds. Giant covalent structures, such as diamond and silicon dioxide, can also be represented using lines to show the strong covalent bonds throughout the structure.

Hydrogen (H₂)

Chlorine (Cl₂)

Oxygen (O₂)

Nitrogen (N₂)

Hydrogen Chloride (HCl)

Water (H₂O)

Ammonia (NH₃)

Methane (CH₄)

Limitations of Diagram Representations

Dot and cross diagrams provide a simplified view of electron sharing, while ball and stick models show the relative positions of atoms in three dimensions. Two-dimensional and three-dimensional diagrams can be limited in representing the true size, shape, and distances between atoms.

Deducing Molecular Formulas

By counting the number of atoms and bonds shown in the diagram, you can determine the molecular formula. For example, if a diagram shows two hydrogen atoms bonded to an oxygen atom, the molecular formula would be H₂O for water.

Conclusion

In conclusion, covalent bonding involves the sharing of electron pairs between atoms. Covalently bonded substances can exist as small molecules, polymers, or giant covalent structures. Small molecules consist of a few atoms bonded together, while polymers are formed by the bonding of many monomers. Giant covalent structures have a vast number of atoms bonded together in a rigid lattice.