Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Macromolecules, or giant covalent structures, consist of a vast number of atoms held together by strong covalent bonds in a regular three-dimensional lattice.
In Diamond, each carbon atom is covalently bonded to other carbon atoms in a tetrahedral arrangement. This rigid structure results in extreme hardness and a very high melting point ().
In Graphite, each carbon atom is bonded to other carbon atoms, forming hexagonal layers. The fourth valence electron is delocalized between layers, allowing graphite to conduct electricity.
The layers in graphite are held together by weak intermolecular forces (van der Waals forces), allowing them to slide over each other, which makes graphite soft and useful as a lubricant.
Silicon dioxide (), also known as silica, has a giant covalent structure similar to diamond. Each Silicon () atom is bonded to Oxygen () atoms, and each Oxygen atom is bonded to Silicon atoms.
Giant covalent structures do not dissolve in water or organic solvents because the attraction between the solvent molecules and the atoms is not strong enough to break the covalent bonds.
📐Formulae
💡Examples
Problem 1:
Explain why Diamond does not conduct electricity, whereas Graphite does, despite both being made of Carbon atoms.
Solution:
In Diamond, all valence electrons of each Carbon atom are involved in covalent bonding ( hybridization), leaving no free electrons. In Graphite, only out of valence electrons are used for bonding ( hybridization). The electron is delocalized and free to move throughout the structure.
Explanation:
Electrical conductivity requires the presence of mobile charge carriers, such as delocalized electrons or ions. Diamond lacks these, while Graphite has delocalized electrons ().
Problem 2:
Compare the melting points of Silicon Dioxide () and Carbon Dioxide ().
Solution:
Silicon Dioxide has a very high melting point (approx. ) because it is a giant macromolecular structure. Carbon Dioxide has a very low melting point ( via sublimation) because it exists as simple discrete molecules.
Explanation:
To melt , strong covalent bonds must be broken. To melt , only weak intermolecular forces between molecules must be overcome, requiring much less energy ().