Mad Teddy's astronomy pages: When is a metal not a metal?

Mad Teddy's web-pages

When is a metal not a metal?

Answer: When you're an astronomer!

"What??!", I hear you cry.

Let me explain. Most of the matter in the universe is in the stars. (Let's not get into the "dark matter" controversy here. ) Stars are made up mostly of hydrogen, which is fusing into helium (initially).

The issue of "dark matter" is addressed in the following page under my "Astronomical stuff" menu, i.e. Quasars: some thoughts.... Scroll a little over halfway down that page to find a link to a web-page which mentions it, in connection with a related issue: the "big bang".

Because hydrogen and helium are the most common substances in the universe (with other elements, produced by further fusion, coming a long way behind), as far as astronomers are concerned, these two are by far the most important. Somewhat arrogantly, they refer rather dismissively to anything else as "metals".

This means that not only lithium (element 3 in the periodic table) and beryllium (element 4) are metals (which they definitely are, in the more usual sense of the word), but also the next few elements: boron, carbon, nitrogen, oxygen, and fluorine.


The chemical elements (of which there are 92 definitely known to occur naturally on Earth, the last being uranium) can be divided into two main classes: metals and non-metals.

UPDATE, 18th July 2006

I've just seen this page by Bill Beaty, which takes issue with that last assertion (regarding 92 elements on Earth). Scroll about two-fifths of the way down to read his article "CORRECTED: there are not 92 elements on Earth".

Having just typed "technetium promethium" into Google, I've turned up this page (among other equally provocative articles!).

MORAL: Don't believe everything you read. Keep your mind OPEN! That way, we can all learn something new every day, and gradually increase the sum of human knowledge and understanding.


UPDATE-WITHIN-AN-UPDATE, 3rd January 2009: I've recently figured out how to render my old computer "YouTube capable"; and just today I've been delighted to find a video of Jefferson Airplane performing "White Rabbit", the last line of which you have just read (above). To see Grace and the gang in full flight, click on the bunny.

To continue:

There are some elements, known as semimetals or metalloids , which can exhibit both metallic and non-metallic properties under certain conditions. These include boron (already mentioned above), silicon, germanium, arsenic, antimony, tellurium, and polonium. (Some sources classify polonium as a metal.)

Some of the metalloids (notably silicon and germanium) are semiconductors, which means that they conduct electricity (fairly) well under some conditions, and rather badly under others. This makes them useful in the manufacture of electronic components such as diodes, transistors, and integrated circuits. In recent years, arsenic has become very important, especially in combination with other elements - notably gallium and phosporus. Some modern very bright light-emitting diodes (LED's) rely heavily on arsenic compounds; and gallium arsenide can convert electrical energy directly into coherent light, thus forming the basis for LASER LED's (which are important in our modern world, as they are what make CD players, CD-ROM drives, DVD players etc. possible).

Profuse apologies in advance for the next few lines. I know it's all a bit silly, but I can't resist it.

When I first heard about arsenic, in some story or other about people being poisoned, I asked my Dad what it was. He said it was "when somebody pinches your bottom" (which, of course, immediately elicited a shocked exclamation from my Mum.)

[If you speak Aussie English, New Zealand English, or any of the many variants of English English, you'll probably understand what this is about. On the other hand, if you're a speaker of American English or similar, it may all be a bit of a mystery to you...]

Sort of reminds me of the kid who wrote in a test that the way to kill an insect is to pinch its borax...

While on the subject: you may like to have a look at these two web-pages (not for those with delicate sensibilities):

>>> Back to business... <<<

By far the majority of the other elements are metals, in the ordinary everyday sense. They tend to be dense, i.e. heavy for their size (although two of them, lithium and sodium, are light enough to float on water). Most of them are solid under normal conditions; mercury is an obvious exception - and gallium melts at just below 30 degrees C, so it too will be a liquid on a really hot day. (A teaspoon made from gallium would be useless for stirring a hot drink. )

Metals are generally malleable (can be hammered into thin sheets) and ductile (can be drawn out as a wire). But by far the most obviously important property that they share is that they conduct electricity quite well - very well, in some cases. Silver is the best conductor; copper is excellent; and gold isn't too far behind, followed by aluminium in fourth place.

The outermost electrons in metal atoms are rather loosely bound, in the sense that in a lump of metal, these electrons are fairly free to roam around within the lump and over its surface. This accounts for the shiny appearance of metals.

Metals are electro-positive - they can readily give up one or more electrons to other atoms which are more electro-negative. This might mean another, less electro-positive, metal; various kinds of true intermetallic compounds may form, with specific ratios of component metals - or they may be alloys of various compositions, in which atomic and inter-atomic geometry plays a part similar in importance to pure electronic bonding. But the more obvious ways metals form compounds is with non-metals.

Non-metallic elements are those which have nearly-filled outer electron shells - as opposed to the situation in metals, which have nearly-empty outer electron shells. Non-metals are "happy" to accept electrons from metals, which are "happy" to donate them. (Excuse the silly anthropomorphism!) Thus ionic bonds can form, and the atoms combine to become a compound.

Just as some metals are more electro-positive than others, so some non-metals are more electro-negative than others. Compounds can certainly be formed from non-metals. The most obvious is water - good old H2O.

There are only 18 (known) non-metallic elements (including hydrogen and helium). Five of them form compounds by accepting just one electron from other atoms. These reactive elements are collectively known as the halogens. The most commonly-known one is chlorine, which is a component of ordinary salt and essential for the life of most if not all animals (including humans).

Chlorine, a green gas, has atomic number 17. The other halogens which have higher atomic numbers are bromine, a red liquid; iodine, a dark bluish-grey waxy solid which produces violet fumes; and astatine, which is a radioactive solid.

Of these, chlorine is the most reactive. By itself, it's quite toxic, and was once used as a poison gas, notably in World War 1. Certain fairly unstable chlorine compounds (which slowly release elemental chlorine) are used in bleach and as a disinfectant to kill micro-organisms in swimming pools - even, in small concentrations, in drinking water.

Going down the list, bromine is less electro-negative, iodine still less so, and astatine still less so again. (Some sources even describe astatine as a metalloid - which brings the number of non-metals down to 17.)

They're all similar to each other in some ways. I don't know much about astatine; it's radio-active and not as well-known as the others. They're all toxic in varying degrees, which means that they may have some medical uses in carefully-controlled quantities. Iodine has long been used in ointments for dressing wounds, as a disinfectant; and it's important to humans in that an iodine deficiency can lead to a medical condition known as goitre (enlargement of the thyroid gland).

They all have similar "chemical" smells, presumably because they interact with olfactory sensors in the nose in similar ways. Interestingly, ozone, O3, a form of oxygen which has three atoms per molecule instead of the usual two, smells a bit like the halogens, with which it shares certain chemical properties.

Ozone is produced by the action of ultra-violet light on oxygen (hence the "ozone layer" in the upper atmosphere), or when a high-voltage spark occurs in ordinary air, as a result of the breakdown and recombination of O2 molecules. It's not considered a good idea to breathe too much of it; freaky people such as myself who have an interest in high-voltage electricity are advised to have a window or door open when generating ozone.

Two interesting and informative web-pages with more details about ozone are here and here.

There is one other halogen: fluorine (atomic number 9), which comes before chlorine in the periodic table. This is seriously dangerous stuff.

It is a pale yellow gas. It attacks just about anything; for example, it can combine with xenon, one of the inert gases, in various proportions to form a number of different compounds. (Admittedly, some such compounds are not particularly stable; but the fact that they will form at all is highly significant.) Many of fluorine's reactions are at least violent, and may often be explosive.

Fluorine was finally isolated by the French chemist Henri Moissan in 1886, by electrolysis - the only way to rip it out of its compounds. It is so electro-negative that no chemical means will shift it. Earlier researchers had managed to isolate simple compounds of fluorine by chemical means - toxic and/or explosive substances which were also very dangerous - but most sources agree that Moissan was the first to isolate the element. He, along with some of these other researchers, suffered injury as a result of exposure to the substance.

Here is a website which has more information about the element.

Fluorine is the most reactive element of them all - and it is definitely a non-metal. To go anthropomorphic again, it "views" everything else - even the other halogens - as electro-positive. (To see a page with some information about compounds containing only chlorine and fluorine, click here .)

So, a definition of an astronomer is: someone who calls fluorine a metal.

Strange people...!

UPDATE, Friday, 2nd January 2009

Having very recently figured out that I can access YouTube videos and suchlike on my computer (a Windows 98 machine, since my old "95" died a while back), I've found to my huge delight that there are several versions of Tom Lehrer's "Elements" song out there for the viewing/listening. So I've decided to put links to a few of them here.

The song, written in 1959, lists all the elements known until then (as far as element 102, nobelium), to the tune of Gilbert and Sullivan's "Modern Major General" (from "Pirates of Penzance"). If you'd like to read the lyrics, click here.

The first video is a very funny cartoon version, with Tom Lehrer's own voice providing the soundtrack. The visuals accompanying the list of elements are brilliantly done; you really have to concentrate to take it all in.

The second has some similarity with the first, but has still photographs of Tom instead of cartoon animation. Again, you need your wits about you to fully appreciate the tightly-packed information on-screen!

The third is done by (I think) a sixteen-year-old girl who gives a very creditable performance, with some amusing text comments scattered throughout.

The fourth is an unashamedly "Milli Vanilli"-style version done by a twelve-year-old. I'm quite sure that to do this as well as it's done here requires a considerable amount of real talent, a strong sense of timing, and a great sense of humour.

The fifth is the icing on the cake. The performer, only four years old, struggles a bit - but perseveres and ultimately pulls off an amazing achievement. Then, to add insult to injury, he confidently reels off the names of all elements discovered since the song was written, in 1959! Absolutely incredible...

There are other versions out there, too. You have to admire people who can do this even tolerably well. Many of the elements have long names, which may be tongue-twisters in their own right - for example, "praseodymium" has six syllables. You try fitting the names of the first 102 elements into a two-minute performance, with or without musical accompaniment!

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One more, just to put the whole matter in some sort of more-or-less serious perspective:

This version again features Tom Lehrer's original version of the song. The very simple graphics accompanying the music simply show an "empty" periodic table being completed, one element at a time, just as each is mentioned.

This version appeals to me, for a very good reason. If I may brag just a little bit, just over a year ago I finally memorized the entire periodic table - at least up as far as some of the recently-discovered elements - to the point where I can actually sit down and write the whole thing out from memory (and if you're not impressed, you jolly well should be! ) - and it's fun to be able to watch the table being filled in, and actually be able to follow the action!

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