Dr. Glaser's "Chemistry is in the News"
To Accompany Bruice, Organic Chemistry, 3/e.
Chapter 1. Electronic Structures and Bonding. Acids and Bases.

Editorial Comments

Atmospheric chemistry is getting all the attention!

In 1995, the Nobel Prize in Chemistry was split threeways to honor Paul Crutzen, Mario Molina, and F. Sherwood Rowland for their work in atmospheric chemistry, particularly concerning the formation and decomposition of ozone. Ozone is, as you all know, critical in filtering the hard UV light out of the sun light. We will return to the issue of ozone again in Chapter 12. Chapter 12 discusses Ultraviolet/Visible Spectroscopy and ozone will be the topic of the news item and of the visualization center for Chapter 12.

The year 1997 brought to the greenhouse gases all the attention they deserve! At a historical conference in the old imperial capital of Kyoto, Japan, the world agreed to cut greenhouse emissions. The major greenhouse gases are carbon dioxide, methane and an assortment of nitrous oxides. But there are many other gases that contribute and some of these can hve large effect even though the gas is present in small amounts only. In July of 2000, for example, articles were published that described the "new" greenhouse gas SF₅CH₃ which is said to be 1000 times more "effective" than methane.

The Asahi press release contains a link methane that talks about methane hydrates on the ocean floors. Under the headline Mass extinction traced to oceanic methane burp, a recent article by CNN.com nature suggested that atmospheric methane might have had catastrophic consequences in the past.

In this context, let's review the structures of some of these pertinent atmospheric gas molecules.

Questions

Question 1: Carbon dioxide is the main man-made greenhouse gas. What do you know about the structure and the bonding of this molecule?

Answer 1: Carbon dioxide is CO₂. The molecule is linear and the C-atom is in the center between two O-atoms. The C-atom is sp-hybridized and C forms a double bond with each of the O-atoms.

Question 2: In the case of carbon dioxide, we pretty much know where it is coming from (mostly from burning fuels) and where it is stored (the oceans) and how this storage is regulated (e.g. cold water dissolves more carbon dioxide and so on). With methane the situation is an entirely different one. We are much less certain about the methane sources and the amount of methane stored. Read the link behind methane in the Asahi press release. What is said about methane in "gas hydrates" and their possible effects on the climate?

Answer 2: Methane bound in hydrates amounts to approximately 3,000 times the volume of methane in the atmosphere! There is insufficient information to judge what geological processes might most affect the stability of hydrates in sediments and the possible release of methane into the atmosphere. Methane might be released from gas hydrates in Arctic sediments as they become warmed during a sea-level rise. This could exacerbate climatic warming and thereby destabilize the climate. Nobody really knows for sure.

Question 3: Of course, you know the structure of methane. Can you give some quantitative data about H-C-H bond angles and the C-H bond length? Can you explain how the theory of hydridization allows to explain the tetrahedral structure?

Answer 3: The angle is 109.5 degrees and the bond length is 110 pm (to be exact, 108.5 pm in the structure shown in the visualization center). The ground state configuration of carbon has only two unpaired electrons. Through "promotion" and "hybridization" four identical singly occupied sp³-hybrid atomic orbitals are created which extend toward the corners of a tetrahedron.

Question 4: Now let's turn briefly to the nitrous oxides. Draw the Lewis structures of NO, of NO₂, and of ON-NO₂. Also draw the Lewis-Kekule structures of the acids HNO₂ and HNO₃. Be sure to get all formal charges right!

Answer 4: Answers can be found in the book.

Chemistry & Society.
Question 5: This question is meant to start a discussion. Perhaps you can discuss this question with your peers (i.e. on the course discussion list). Here is the question: How effective do you think "emissions trading" is going to be?