Final answer:
Diamond and graphite have different properties due to their distinct atomic structures. Diamond's carbon atoms form a rigid 3D lattice, making it hard and clear, while graphite's layered structure results in a softer and more opaque material. This structural variation is due to the different bonding arrangements of carbon atoms, yet each atom maintains four bonds as per the octet rule.
Step-by-step explanation:
The difference in properties between diamond and graphite, despite both being made of pure carbon, is attributed to the different arrangement of carbon atoms within their structures. Diamond consists of sp3 hybridized carbon atoms each bonded to four other carbon atoms in a tetrahedral array, forming a giant molecule with a three-dimensional network. This contributes to diamond's hard and transparent characteristics. On the other hand, graphite is composed of layers of six-membered rings of carbon atoms. These layers are weakly bonded, which allows them to slide over each other, making graphite soft and opaque, giving it excellent lubricating and electrical conductivity properties.
The ability of graphite to be transformed into diamond at very high temperatures and pressures represents a physical change, as it involves a change in the structure of the carbon atoms without altering their chemical nature. The individual carbon atoms form four bonds regardless of the allotrope, following the octet rule.