HS Chemistry - Chemical Bonding

Overview of The Page

This page will cover:

• What are allotropes?
• What are a few allotropes of Carbon?

Allotropes

Allotropes are different molecular arrangements of the same element $i.e. the elements are arranged differently, and the molecules have different structures despite having the same elements$.

A common example is carbon, which has three main allotropes: graphite, diamond, and fullerenes.

Graphite

Graphite is the most stable form of carbon. The carbon atoms are arranged in hexagonal structures, with each carbon atom covalently bonded to three others.

Each carbon atom has 4 valence electrons, but each carbon atom in graphite is only bonded to 3 other carbon atoms, and there are no double bonds. That leaves an extra, delocalized electron which can wander throughout the substance. This allows graphite to conduct electricity.

Graphite is arranged in multiple layers, connected by weak intermolecular forces:

Since the forces holding these layers together are very weak, they can easily be broken. Thus, graphite can be cut very easily, separating its layers.

However, the forces within each layer are quite strong, as each carbon atom is bonded to three others. This causes graphite to have high melting and boiling points, as it takes a lot of energy to break these bonds.

Diamond

In diamond, the carbon atoms are arranged in a crystalline structure, with each carbon atom covalently bonded to four other carbon atoms in a tetrahedral geometry.

Not only does this produce diamond's crystal structure, but since each carbon atom is bonded to four others, it has very high melting and boiling points. The crystal structure also makes it very hard.

Fullerenes

In fullerenes, the carbon atoms are arranged in hexagonal structures, with each carbon atom covalently bonded to three others.

But it's different from graphite because instead of each carbon atom having 1 delocalized electron, each carbon atom forms 1 double bond. This means that fullerenes can't conduct electricity.

Carbon atoms in fullerenes are arranged in a continuing pattern of hexagons, rather than in layers of hexagons $which is how they are arranged in graphite$. Therefore, fullerenes can't easily be cut or split apart.

Since each carbon atom is bonded to three others, the forces of attraction are quite strong. It takes a lot of energy to break these bonds, which is why fullerenes have high melting and boiling points.

However, fullerenes are malleable - the "hexagons" can easily be rotated relative to one another, allowing fullerene to easily change its shape.