general chemistry

Survivor: Mechanisms (now accepting logo submissions)

gibbsfreepassI read an interesting article in May’s issue of J. Chem. Ed. titled “Can Reaction Mechanisms Be Proven?” by Allen Buskirk and Hediyeh Baradaran of BYU.  Intriguing.  So I pop open the pdf and a Note from the Editor is boxed at the top of the page before the article starts.  It says:

“Can Reaction Mechanisms Be Proven?” generated spirited responses from its reviewers. The reviews were approximately evenly divided, and all were of very high quality. The authors agreed with the editor’s proposal that the reviewers convert their reviews into rebuttals or affirmations of the authors’ position for publication along with the article, which has been revised based on the reviews. Most agreed to such a process and their comments appear here. We hope that publication of this paper and well-reasoned rebuttals such as those provided here will initiate a wide-ranging discussion. JCE will provide an online forum for further discussion of the issue. Our hope is that both faculty and students will contribute their opinions and ideas to this discussion. -JWM

Huh.  You don’t usually hear about that happening too often.  So now I had to read the article.  It’s pretty fascinating, and I encourage you to read it all.  I’ll summarize and give my thoughts below the jump

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My Attempt At a Periodic Table

Inspired by azmanam’s recent post, Alternative Periodic Tables, I’ve decided to make my own periodic table. I freely admit I didn’t improve much on the old Mendeleev design. The only unique difference with this table is the color coding for the valence electrons

periodic-table4

The Basics
s-blocks are blue, d-blocks are green, p-blocks are shades of purple-pink, f-blocks are red. Black are for the elements that have never been studied chemically.

The Exceptions
The d-metals that are missing an s-electron in their octet are teal (green + blue). The f-metals that have an extra d-electron are brown (green + red). The super brights Palladium and Thorium gained or lost two electrons not in their native octet.

It was always difficult for me to remember where in the periodic table the electron configurations do not conform to what I would naively assume. I would hope this type of periodic table keeps it more in the mind of students.

Mitch

By May 3, 2009 14 comments general chemistry

Alternative Periodic Tables (Updated. Now with a Final Thought!)

There’s an article in the current issue of Nature Chemistry that discusses some alternative ways of depicting the periodicity of the elements. There’s the IUPAC recognized Mendeleevian periodic table that everyone knows. There’s probably 3 in eyesight of you right now, isn’t there?
mendeleev(click for larger)

d

d

d

But how many alternative periodic tables can you think of.  Hint: there’s A LOT.  More below the jump.

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By April 26, 2009 100 comments general chemistry

Teen Chemist and Splenda

For as long as artificial sweeteners have been used, there has been a varying level of controversy over the safety of their use; both for humans and the environment in general. Saccharin and Aspartame have been plagued by health concerns raised by researchers for decades. Most studies have shown that only in very high concentrations are they dangerous, however few long term (>10 years) studies have been completed, so lower dose, chronic exposure has yet to be rigorously  investigated. Currently, most diet sodas use aspartame and saccharin, including my favorite, Coke Zero. Another very popular sugar substitute, sucralose has begun to steal the spotlight away from aspartame in recent years, taking over popular drinks like Crystal Light, Tim Horton’s and Starbucks coffee.

The chlorinated sugar substitute called sucralose 200px-sucralose2svg(commercially marketed as Splenda (TM)) was first synthesized in 1976, as part of a collaboration between Queen Elizabeth College in London and the Tate and Lyle Chemical Company. It is manufactured by the selective chlorination of sucrose, in which three of the hydroxyl groups are replaced with chlorine atoms. Supposedly the graduate student, Shashikant Phadnis, working on the synthesis misunderstood his professor’s request to test the chemical as a request to taste the chemical. Just goes to show, sometimes to make a lucrative discovery, a chemist must take the ultimate test!

Whatever happened, it has been found that Sucralose is approximately 600 times sweeter than sucrose, and since being introduced in the USA in 1998, has become one of the leading sweeteners on the market. One of the main reasons for this is that studies have shown that sucralose is highly stable; it doesn’t break down easily due to heat so cooking with it is safe. It also doesn’t dechlorinate over time, photo degrade under visible light, or biodegrade with common bacteria. It is also very insoluble in fat cells, so all of us Americans don’t have to worry about getting a heart attack on the treadmill (at least not from sucralose!). In fact, sucralose is so darn stable, it doesn’t even get broken down in waste treatment plants.

Meet Smitha Ramakrishna, a senior at Corona del Sol High School in Chandler, Arizona, who has been doing research at Arizona State University about sucralose’s inability to be broken down and how this make affect the environment. At only 17 years of age, she has been researching sucralose for nearly 2 years, as part of her greater goal of trying to help with global water issues. She also founded an organization named AWAKE, which is dedicated to increasing her community’s awareness about water-related issues.

She has found that after subjecting sucralose to treatments similar to those used by waste water treatment plants, the sweetener resisted bacterial digestion. Only after a long time and under UV irradiation in the presence of high concentrations of titanium oxide (TiO2) did the sugar break down. Considering that few plants use these methods, the majority of sucralose in wastewater enters the ecosystem. She doesn’t say for sure what effect this will have, but says that preliminary studies suggest high concentrations of sucralose may poison fish.

See more here: That Splenda you’re drinking will be in our water supply for a while

Personally, I think people should use xylitol more. First studied in the 1970’s, almost no negative effects have been found due to ingestion of even 400+ grams a day (imagine 400+ grams of sugar! BLECH!) and many positive health effects have been proven ranging from plaque-reducing effects to boosting your immune system. It is about as sweet as sucrose, and has 2/3 the caloric content.

That said, I am still gonna go get me a coke zero.