CdS has a band gap of 2.4 eV. If large crystals of CdS are illuminated with ultraviolet light, they emit light equal to the band gap energy. (a) What color is the emitted light?
Ch.12 - Solids and Modern Materials
Chapter 12, Problem 101
Which statement correctly describes a difference between graphene and graphite? (a) Graphene is a molecule but graphite is not. (b) Graphene is a single sheet of carbon atoms and graphite contains many, and larger, sheets of carbon atoms. (c) Graphene is an insulator but graphite is a metal. (d) Graphite is pure carbon but graphene is not. (e) The carbons are sp2 hybridized in graphene but sp3 hybridized in graphite.

1
Understand the structure of graphene: Graphene is a single layer of carbon atoms arranged in a two-dimensional honeycomb lattice.
Understand the structure of graphite: Graphite consists of many layers of graphene stacked on top of each other, with weak van der Waals forces between the layers.
Compare the structures: Graphene is a single sheet, while graphite is composed of multiple sheets of graphene.
Consider the hybridization: Both graphene and graphite have carbon atoms that are sp2 hybridized, not sp3.
Evaluate the options: Option (b) correctly describes the difference between graphene and graphite, as graphene is a single sheet and graphite contains many sheets.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Structure of Graphene and Graphite
Graphene is a single layer of carbon atoms arranged in a two-dimensional honeycomb lattice, while graphite consists of multiple layers of graphene stacked together. This structural difference leads to distinct physical properties, such as electrical conductivity and mechanical strength, making graphene a highly sought-after material in various applications.
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Hybridization of Carbon Atoms
In graphene, each carbon atom is sp2 hybridized, meaning it forms three sigma bonds with neighboring carbon atoms and has one unhybridized p orbital that contributes to delocalized pi bonding. In contrast, graphite's carbon atoms are also primarily sp2 hybridized, allowing for similar bonding characteristics, but the presence of multiple layers affects the overall properties of the material.
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Electrical Conductivity
Graphene is an excellent conductor of electricity due to its structure, which allows for the free movement of electrons across its surface. Graphite, while also a good conductor, exhibits different conductivity characteristics because of its layered structure, which can impede electron flow between layers. Understanding these differences is crucial for applications in electronics and materials science.
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Related Practice
Textbook Question
Textbook Question
CdS has a band gap of 2.4 eV. If large crystals of CdS are illuminated with ultraviolet light, they emit light equal to the band gap energy. (b) Would appropriately sized CdS quantum dots be able to emit blue light?
Textbook Question
CdS has a band gap of 2.4 eV. If large crystals of CdS are illuminated with ultraviolet light, they emit light equal to the band gap energy. (c) What about red light?
Textbook Question
Selected chlorides have the following melting points: NaCl (801 °C), MgCl2 (714 °C), PCl3 (-94 °C), SCl2 (-121 °C) (a) For each compound, indicate what type its solid form is (molecular, metallic, ionic, or covalent-network).