Question

Which statement is inconsistent about graphite? (a) A two dimensional sheet like structure in which each C atom uses sp \(^{2}\) hybrid orbitals. (b) Pi electrons are delocalized and free to move perpendicular to the plane of the hexagonal sheets. (c) Carbon sheets are separated by a distance of \(335 \mathrm{pm}\) and are held together by weak London dispe sion forces. (d) Electrical conductivity parallel to the planar sheets is \(10^{20}\) times greater than the conductivity of diamond.

Short answer

Option (d) is inconsistent about graphite.

Step-by-step solution

Understanding Graphite Structure

Graphite consists of layers where each carbon atom forms three sigma bonds using sp\(^{2}\) hybridized orbitals, with the fourth electron delocalized in a pi-bonding system. This sheet-like structure supports delocalization of electrons, providing electrical conductivity parallel to the layers.

Evaluating Option (a)

Option (a) describes the sp\(^{2}\) hybridization of carbon atoms in graphite, forming a two-dimensional sheet-like structure. This statement is consistent with graphite's known structure and properties.

Analyzing Option (b)

In option (b), the pi electrons of graphite are indeed delocalized and free to move over the planes, contributing to the electrical conductivity of graphite parallel to the layers. This statement is consistent with the properties of graphite.

Assessing Option (c)

Option (c) states that carbon sheets are separated by 335 pm and held by weak London dispersion forces, which is consistent with graphite's layer structure and the weak forces between the layers.

Examining Option (d)

Option (d) asserts that graphite's electrical conductivity is \(10^{20}\) times greater than that of diamond. This discrepancy is exaggerated, as while graphite is a good conductor due to its delocalized electrons, diamond, being an insulator, does not exhibit such a vast difference. Hence, this statement is inconsistent.

Key concepts

sp2 Hybridization

In the structure of graphite, each carbon atom undergoes hybridization to form sp\(^{2}\) hybrid orbitals. This is a specific type of hybridization where one 's' orbital combines with two 'p' orbitals to create three sp\(^{2}\) orbitals.

These orbitals are oriented in a trigonal planar shape around each carbon atom, forming a 120-degree angle with each other. This creates a two-dimensional hexagonal sheet-like structure, often visualized as a honeycomb pattern.

• Each carbon atom forms three sigma bonds using these sp\(^{2}\) hybridized orbitals.
• The fourth electron of each carbon atom resides in a 'p' orbital, perpendicular to the plane of the hexagon, allowing for pi-bonding.

This arrangement leads to a strong covalent bonding within the layers, contributing to graphite's strength and stability.

Electrical Conductivity in Graphite

Graphite is known for its remarkable electrical conductivity, which is closely related to its structure and bonding.

In graphite, the sp\(^{2}\) hybridization of carbon atoms leaves one electron in a p-orbital, which overlaps with those of neighboring carbon atoms. This overlapping forms a pi-bonding system across the sheets, facilitating the delocalization of electrons.

• The pi electrons are free to move over the plane of the carbon sheets.
• This delocalized electron movement allows graphite to conduct electricity efficiently.
• Graphite conducts electricity parallel to the planes of carbon sheets.

This ability to conduct electricity makes graphite useful in various applications, such as in batteries and electrodes.

London Dispersion Forces in Graphite

Although the layers within graphite are held together strongly by covalent bonds, the interaction between these layers is much weaker.

The sheets of carbon atoms are separated by a distance of approximately 335 pm and are held together by London dispersion forces.

• These are weak intermolecular forces occurring due to temporary dipoles that form when electrons momentarily cluster in one part of a molecule.
• The London dispersion forces are the weakest type of van der Waals forces, but in the case of graphite, they provide sufficient attraction to maintain the layer arrangement without disrupting its conductivity or stability.

This stacking structure enables graphite to easily cleave or slide over the adjacent layers, which imparts lubricating properties to graphite, making it useful in products like pencil lead and as a dry lubricant.