Chapter 9, Problem 72SCQ

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

# The following problem is taken from the Theoretical Examination of the 44th annual International Chemistry Olympiad in 2012, a competition attended by four secondary school students from each of about 70 countries. (Used with permission.)Graphene is a sheet of carbon atoms arranged in a two-dimensional honeycomb pattern. It can be considered as an extreme case of a polyaromatic hydrocarbon with essentially infinite length in two dimensions. Graphene has remarkable strength, flexibility, and electrical properties. The Nobel Prize for Physics was awarded in 2010 to Andre Geim and Konstantin Novoselov for groundbreaking experiments on graphene. A section of the graphene sheet is shown below.The area of one hexagonal 6-carbon unit is ~52400 pm2. Calculate the number of π electrons in a tiny 25 nm × 25 nm sheet of graphene. For this problem you can ignore edge electrons (i.e, those outside the full hexagons in the picture).

Interpretation Introduction

Interpretation:

The number of π electrons in a tiny 25nm×25nm sheet of graphene has to be determined if the area of one hexagonal 6 - carbon unit is approximately 52400pm2

Concept Introduction

Graphene:

• It is one of the allotropes of carbon.
• It exists as a two-dimensional planar sheet.
• It has a hexagonal arrangement in which each carbon atom is bonded to three other atoms.
• Possess good thermal, chemical and optical properties.
Explanation

Given data,

Areaâ€‰=â€‰52400â€‰pm2Lxâ€‰=â€‰25â€‰nmâ€‰=â€‰25000â€‰pmLyâ€‰=â€‰25â€‰nmâ€‰=â€‰25000â€‰pm

The number of hexagonal units in the graphene sheet can be calculated by the equation given below:

Nunitsâ€‰=â€‰Areaâ€‰grapheneAreaâ€‰unit

Nunitsâ€‰

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