Here's a breakdown of key features:
* Large molecules: The fundamental units of the crystal are molecules, which are formed by covalent bonds within the molecule.
* Covalent bonding: Strong covalent bonds connect the atoms within the molecule, and the molecules are held together in a continuous network by further covalent bonds.
* Extended structure: There are no distinct molecular units. Instead, the covalent bonds form a continuous, extended structure, making the entire crystal essentially one giant molecule.
* High melting and boiling points: Due to the strong covalent bonds, giant molecular crystals have high melting and boiling points. They require significant energy to break the bonds and separate the molecules.
Examples:
* Diamond: Carbon atoms are connected in a tetrahedral arrangement by strong covalent bonds. This creates a giant molecular crystal with exceptional hardness and high melting point.
* Silicon dioxide (SiO2): The basic unit is the SiO4 tetrahedron, which forms a three-dimensional network with strong covalent bonds. This gives silica its high melting point and brittle nature.
* Graphite: Carbon atoms form layers held together by weaker van der Waals forces, while within the layers, strong covalent bonds create a giant molecular structure. This explains the layered structure and different properties of graphite compared to diamond.
Key differences from ionic and metallic crystals:
* Ionic crystals: Held together by electrostatic forces between ions.
* Metallic crystals: Held together by delocalized electrons in a "sea" of electrons.
In contrast, giant molecular crystals are solely held together by a continuous network of covalent bonds.
Understanding the properties of giant molecular crystals is essential in fields like materials science, where their unique characteristics, like high hardness and thermal stability, make them valuable for applications like semiconductors and industrial tools.
