Question

What is the number of free electrons present on each carbon atom in graphite? (a) Zero (b) 1 (c) 2 (d) 3

Short answer

(b) Each carbon atom in graphite has 1 free electron.

Step-by-step solution

Understanding Carbon's Bonding in Graphite

Graphite is composed of layers of carbon atoms. Each carbon atom forms three covalent bonds with neighboring carbon atoms in a single plane. This allows each carbon atom to use three out of its four valence electrons for bonding within the plane.

Identifying Free Electrons

Every carbon atom in graphite has four valence electrons. After forming three bonds, one electron per carbon atom does not participate in bonding. This electron is delocalized across the graphite layer, contributing to electrical conductivity.

Conclusion on Free Electrons per Carbon Atom

Since each carbon atom in graphite contributes one electron to a conduction band in the material, there is one free electron per carbon atom. This delocalization is characteristic of the strong electrical conductivity observed in graphite.

Key concepts

Free Electrons in Carbon

In graphite, carbon atoms exhibit a fascinating arrangement that impacts their electronic behavior. Each carbon atom has a total of four valence electrons available for bonding.
However, due to the unique structure of graphite, only three of these valence electrons participate in forming covalent bonds with neighboring carbon atoms within the same layer.

• The fourth valence electron does not participate in these bonds and remains "free."
• This free electron becomes delocalized, meaning it can move freely across the entire layer of carbon atoms.

This delocalization of electrons contributes significantly to the electrical conductivity of graphite, making it an efficient conductor of electricity. The presence of these free electrons is crucial to many of graphite's unique properties.

Graphite Structure

Graphite has a distinct layered structure made up of carbon atoms arranged in a hexagonal lattice. These layers, akin to sheets, are stacked on top of each other, with weak van der Waals forces holding the sheets together.

• Each sheet of carbon atoms forms a two-dimensional plane, with each carbon atom covalently bonded to three others, creating a flat "honeycomb" pattern.
• The planes have strong intralayer bonds but are lightly bonded to adjacent layers, allowing them to slide over one another easily.

This layered arrangement is responsible for some of graphite's interesting characteristics. For example, it acts as a lubricant due to these sliding layers. The structural design also aids in efficient thermal and electrical conduction across the layers.

Covalent Bonds in Graphite

In the graphite structure, carbon atoms bond covalently with their neighbors in the same layer. Each carbon atom engages in three covalent bonds, utilizing three of its four valence electrons. This type of bonding produces robust connections within the plane.

• The triangular planar shape created by these bonds gives each carbon atom a degree of stability and forms a consistent hexagonal lattice across the plane.
• The strength of these covalent bonds is responsible for the structural integrity and durability of individual graphite sheets.

Though the bonds are strong within the plane, the layers themselves are held together lightly, allowing them to easily detach, which gives graphite its characteristic softness. This covalent bonding is a defining feature of graphite, underpinning its physical and chemical behavior.