What type of bonding exists in (i) calcium fluoride (CaF2), (ii) bronze, and (iii) graphene?
The correct answer and explanation is:
- Calcium Fluoride (CaF₂): Calcium fluoride exhibits ionic bonding. In this compound, calcium (Ca) donates two electrons to form Ca²⁺ ions, while each fluorine (F) atom accepts one electron to form F⁻ ions. The electrostatic attraction between the positively charged calcium ions and the negatively charged fluoride ions holds the structure together. Calcium fluoride forms a crystalline lattice, where the ions are arranged in a repeating pattern to minimize energy. Ionic bonds are generally strong and result in compounds with high melting and boiling points, as well as the ability to conduct electricity when melted or dissolved in water, due to the mobility of the ions.
- Bronze: Bronze is an alloy primarily composed of copper and tin, with other elements sometimes added for specific properties. The bonding in bronze involves metallic bonding. In this type of bonding, atoms of copper and tin in the alloy form a “sea of electrons” around fixed metal cations. These delocalized electrons are free to move through the structure, which contributes to the high electrical conductivity, malleability, and ductility of the alloy. The metal atoms are held together by the electrostatic attraction between the positive metal ions and the delocalized electrons. This type of bonding allows bronze to be shaped into various forms, which is why it has been used historically for coins, sculptures, and tools.
- Graphene: Graphene exhibits covalent bonding. It is a single layer of carbon atoms arranged in a hexagonal lattice. Each carbon atom in graphene forms strong covalent bonds with three adjacent carbon atoms, creating a stable and rigid sheet. These covalent bonds are formed by the sharing of electrons between atoms. Graphene is a remarkable material due to its strength, conductivity, and flexibility. The covalent bonds between the carbon atoms make the structure incredibly strong, yet the delocalized π-electrons (from the fourth electron of each carbon atom) allow graphene to conduct electricity efficiently. The bonding in graphene gives it unique mechanical and electrical properties, making it useful for applications in electronics, materials science, and nanotechnology.