It's Just a Phase

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Allotropes are all the rage? Or at least sending Conan O'Brien over a very funny edge! The bit was inspired by this article in the NY Times science section. I'm not nearly this riveting when I lecture about allotropes, I've got to admit.

O'Brien gets the chemistry nearly right. My only quibble would be that he calls the different forms (the diagrams are the real thing, by the way) different phases, which they aren't really. They are technically allotropes, different structural forms within the same phase or state of matter. The quintessential example is the allotropes of solid carbon, graphite and diamond and a few others. All that said, when you draw a phase diagram for an element, you show the allotropes on it, and many chemists would characterize the change from one allotrope to another as a phase change.

Oxygen has some fascinating solid allotropes, including one that is a blue solid at room temperature!

Shell Games

I'm an unrepentant Trekkie, I'll admit it. Remember when Spock, Scotty, Uhura, Sulu, Chekov, Kirk and McCoy went back in time to San Francisco to rescue the humpback whales? Scotty got a local company to whip up some transparent aluminum to use to build a whale tank in the ship to bring the whales back to save the Earth.

In the latest issue of Nature, Robert Richie's group at Lawrence Berkeley Labs reports that they have created a composite material that mimics aluminum alloys in strength. Following nature's lead, they use ice as a template to build layers aluminum oxide and polymethacrylate into a strong ceramic similar in structure to nacre - the stuff of which shells are made.

The materials extraordinary strength relative to the component materials is due to the stacking of the layers, which make it difficult for macroscopic cracks to form. Could this type of process lead to transparent aluminum alloy?

Grapes of Wrath

My youngest came home from a father-son event with a new interest in healthy foods. I put grapes on the table with dinner. "There are grapes for dinner," he exclaimed. Who are you and what have you done with son? ran through my mind.

At the end of dinner he puts two grapes on his plate and carefully cuts them nearly in half. Then he ducks into the kitchen. "Come on, Mom!" Warm grapes? He'd eaten all the chicken, there was nothing left on his plate to veronique.

He hits the start button and suddenly the grapes start arcing, and one actually bursts momentarily into flame. I'm stunned. No metal, but the arcing is clear. We try various experiments - do you have to leave the grapes connected (no), does it work with other things (carrots), can you char a grape (yes).

What's going on? Hang on, we were producing plasmas in the kitchen. Not the kind that circulates in your veins, but the kind that stars are made out of. Plasma is often called the 4th phase of matter - the iconic triad being solid, liquid and gas. (There are many other phases in which substances can exist, in fact - such as liquid crystals and supercritical fluids.)

Plasmas are gases in which a large number of electron are "free", rather than associated with a molecule or atom.

I'm still trying to come to grips with the idea that I can create a (very tiny) ball of plasma in my kitchen.

(Read more in the paper : "Microwave Mischief and Madness" by H. Hosack, N. Marler, D. MacIsaac of Northern Arizona University, The Physics Teacher 40, 14 (2002).

Protecting Groups

The whole family was at camp last week, living in tents, sleeping on cots, eating in the mess hall. Every camp has them, squirrels and chipmunks that survive on the crumbs of campers' treats (or sometimes the whole banana). We were warned - no food in the tents except in metal boxes.

The boys had the tent next door to ours. I came back from dinner one night to find a very happy squirrel just making off with a chip container from the kids tent. At which point I remembered the dried fruit I'd left in my pack after the morning hike. Whew...it was still there. The rodents had been attracted to the far more tasty snack leavings next door. The boys tent is serving as (a chemist would say) a protecting group.

Chemical protecting groups work similarly. Say you have two sites on a molecule that can react with a reagent, but you only want one to undergo the reaction. If you can put a protecting group on the site you want left unmolested, like a cover, you can run the reaction, change the other site and then take off the protecting group. (See the scheme for an example.)

It works wonderfully for many reactions, and is keeping my pack safe from marauders.

Weird Words of Science: isotope

The periodic table is the map of the chemical world. Columns collect atoms which share properties - all of the elements on the far right - He, Ne, Ar… - are all gases and all nearly chemically inert. The region at the bottom harbors elements more likely to be radioactive. Metals pool in the middle.

Each atom of an element has a characteristic number of protons - positively charged particles - in their nucleus. An atom with five protons is boron. One with 82? Lead.

Most atoms also have a number of uncharged particles - neutrons - in their nuclei as well. The sum of the number of protons and neutrons in a given nucleus is called its mass number. A boron atom with six neutrons has a mass number of 11: five protons and six neutrons. Take away a neutron and it’s still boron, but the mass number is now 10.

Atoms with different mass numbers but the same number of protons are termed isotopes. Most elements have several naturally occuring isotopes. The most abundant form of the element carbon has a mass number of 12. One percent of carbon atoms, however, have an extra neutron and a mass number of 13.

Scottish novelist and physician Margaret Todd coined the term for her distant relative Frederick Soddy at a dinner party in 1913. He had described his research to her and she responded that any good discovery need a Greek term to describe it. She suggested combining the Greek “iso” for same and “topos” for place - to emphasize that the mass number of an element doesn’t affect it’s place in the periodic table: argon-36 and argon-40 are both inert gases. Soddy went on to win the Nobel Prize in 1921 for his discovery - perhaps because his distant relation had coined him a such good term?

Writing in Santa Fe

In about 8 hours, I should be taking off for Santa Fe and the 2008 Santa Fe Science Writing Workshop. I'm bringing some of the work I've done on the blog, trying to shape a longer and coherent narrative. There are about 40 students coming - from a range of backgrounds. Scientists, journalists, students. My instructor will be Laura Helmuth - the science editor for the Smithsonian.

How to tell if you're really a chemist

You pronounce unionized as UN-ionized not union-ized.
When you hear the word mole, you don't think of an animal.
Milli is a prefix, not a girl's name.

This Sceptical Chemist blog post suggests a new test to tell if you're really a chemist. What do you see when you look at this illustration by Joon Mo Kang? If the first things you see are five bonds to carbon, and three bonds to a hydrogen, you're a chemist. If that's all you see - you are really a chemist.

A couple of chemists missed the point of the illustration so completely they wrote to the NY Times to let them know of their chemical illiteracy. Another blogger was also vexed by the nonsensical molecule.

I'll admit it -- I saw five bonds.

The Grecian Bends: Ladies' Corsets and Henry's Law

In an earlier post I suggested there was a connection between ladies' corsets and Henry's Law. A general statement of Henry's Law is that the solubility of a gas in a liquid depends on the pressure of the gas above the liquid. An everyday example is soda. A can of soda is pressurized by exposing it to carbon dioxide having equivalent of about 2.5 times atmospheric pressure at room temperature. When you quickly lower the pressure of carbon dioxide over the liquid, say by opening the can, the solubility decreases and the gas adjusts by rapidly coming out of solution. Fizzing results (and eventually the soda goes flat).

When a diver dives the pressure of the gases breathed increases, and the amount dissolved in the blood increases. Diving to just 50 feet increases the total pressure to roughly that of the carbonated soda! Rapidly ascending reduces the pressure, just like opening the can of soda, and the gas rapidly comes out of solution - the diver's blood can "fizz". Bubbles in the blood and body tissues are clearly not a great thing, and the physiological effects range from the relatively minor (bubbles in the skin layers) and joint pain, to potentially lethal embolisms in the brain and lungs.

This phenomenon was first observed by Robert Boyle in 1670 who noted the formation of bubbles in the eyes of a snake that had been placed in a high pressure environment, then rapidly decompressed. "I once observed a viper furiously tortured in our exhausted receiver… that had manifestly a conspicuous bubble moving to and fro in the waterish humour of one of its eyes." Before the effects was widely understood, many construction workers suffered from "caisson workers' disease" while working in pressurized environments (caissons) under rivers.

Dive tables - a schedule for ascending from a dive that reduces the chance of decompression sickness - were first created for use by British Navy divers in the early 20th century. How do whales and dolphins cope without dive tables? Half-mile deep, hour long dives are not uncommon - and a rapid ascent from depth could cause a massive case of the bends. They may not be immune - recently researchers have found evidence for chronic decompression injuries in sperm whales. The whale bone in the photo above shows evidence of dysbaric osteonecrosis (bone death caused by rapid decompression).

What does this all have to do with ladies' corsets? In the 1870s tight corsets and big bustles were all the rage. The posture forced upon women wearing these fashionable undergarments was called the Grecian Bend. As decompression injuries caused a similar posture, workers on the Brooklyn Bridge christened the syndrome "the Grecian bends", soon shortened to "the bends".

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The photograph of the whale bone is by Tom Kleindinst, Woods Hole Oceanographic Institution and is used with permission.

The image of the Grecian Bends is from the Library of Congress

Concentrated Chemistry: American Chemical Society National Meeting

The American Chemical Society national meeting is on in New Orleans this week. Somewhere on the order of 10,000 chemists will be here for at least some of the week - it's noticeable on the streets to be sure.

The Nature Chemistry group win the prize for most challenging travel. Read the teaser at the Sceptical Chymist - and place your bet on whether United Airlines will get them home again. A road trip to London isn't going to be the solution to return travel woes (unless that Bering Strait tunnel project gets off the drawing board much sooner than anticipated...).

The ACS has an oral history project going...and I'm signed up to be videotaped this afternoon.

My favorite t-shirt seen at the meeting: The name's Bond. Ionic bond. Taken, not shared.

Random Facts about Ludwig B.

Not that Ludwig B. - the other Ludwig B: Ludwig Boltzmann, an Austrian physicist.

Boltzmann's name is familiar to many science students through the eponymous constant: 1.381 x 10^-23 Joules/mole-Kelvin, which appears in many equations. The constant (usually written as k) arises from the proportionality between the absolute entropy of a system (S) and the number of possible arrangements of that system (W). Boltzmann's expression of the entropy, S=k ln W, is inscribed on Boltzmann’s tombstone in Vienna, Austria. Boltzmann did not write it in this form, however, Planck did.

Boltzmann also has two other equations named for him, the first is a diffusion equation used in neutron transport theory and the second describes particles in a gravitational field. In 1904, Boltzmann gave lectures on mathematics at the World’s Fair in St. Louis. He was also a popular lecturer in philosophy at the University of Vienna. Boltzmann is considered the founder of statistical mechanics, and a strong proponent of the “atomistic” view that underscored the importance of understanding the behavior of atoms and molecules in order to understand the bulk.

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Loosely, the entropy is a measure of the "randomness" in a system.