Moseley

An early physics pioneer you rarely hear about is Henry Moseley, who died 100 years ago today. Moseley made an important discovery now called "Moseley's Law."

Up until Moseley's time, chemical elements in the iconic Periodic Table were arranged according to weight. There was other rhyme and reason to the arrangement of elements in the Table, but no true understanding of their masses beyond: things get heavier. There was hope that atomic mass would reveal something fundamental about physics, and the 1914 Nobel Prize went to Harvard's T. W. Richards for his careful and methodical measurements of atomic weights.

Moseley showed that by shining X-rays onto atomic samples, he got a distinct integer value for each element which he called Z. Others before Moseley -- namely Bunsen and Kirchoff -- had shown how unseen atoms could be "seen" and identified by burning them in flames, but Moseley's experiments were beautifully simple and related all elements together with their Z-values instead of getting a unique "fingerprint" for each. Moseley's law is still used to identify elements in deep space.

Exactly what Z was had only been postulated a few years earlier. Niels Bohr had shown that Z was the nuclear charge (1 for the hydrogen atom) and Ernest Rutherford had suggested that Z for heavy atoms might be about half an element's atomic weight. A Dutchman, Antonius van den Broek had suggested--without proof-- that Z was an element's "atomic number." Moseley proved it.

Good ideas need good proof to become good science.

The Periodic Table was never the same after Moseley.

Henry Moseley probably should have gotten the 1915 or 1916 Nobel Prize in Physics, but he was killed by a Turkish bullet at Gallipoli at the age of 27.   

Henry Moseley (1887-1915)

Isaac Asimov wrote: "In view of what he [Moseley] might still have accomplished ... his death might well have been the most costly single death of the War to mankind generally."

Notes on "The Disappearing Spoon"

[continuation in part]

I'm reading Sam Kean's book "The Disappearing Spoon" and posting comments about it. I'm on page 29:

Reading the periodic table across each row reveals a lot about the elements, but that's only part of the story, and not even the best part. Elements in the same column, latitudinal neighbors, are actually far more intimately related than horizontal neighbors. People are used to reading from left to right (or right to left) in virtually every human language, but reading the periodic table up and down, column by column, as in some forms of Japanese, is actually more significant. Doing so reveals a rich subtext of relationships among elements, including unexpected rivalries and antagonisms. The periodic table has its own grammar, and reading between its lines reveals whole new stories. 

Very very nice. I call the up down periodic relationship between elements "rhyming;" each element rhymes with the one above and below it.  The table is written in 2n² meter, where n = 1, 2, 3, 4... link
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Next up, Chapter 2: "Near Twins and Black Sheep: The genealogy of Elements C, Si, Ge" wherein I pretend to get nasty.

More Notes on "The Disappearing Spoon"

[continuation in part]

I'm reading a book and posting comments about it:

Sam Kean wrote a book a couple years back called "The Disappearing Spoon And Other True Tales Of Madness, Love, And The History Of The World From The Periodic Table Of The Elements." 

I am at:

Part I   "Orientation: Column By Column, Row by Row"

1. Geography Is Destiny: He, B, Sb, Tm, O, Ho
_____________________________

This chapter is an excellent introduction but risks alienation from the start. Page 12, line 1:

Probably the biggest frustration for many students was that the people who got the periodic chart, who could really unpack how it worked, could pull so many facts from it with such dweeby nonchalance.

Dweeb: noun: an insignificant student who is ridiculed as being affected or studying excessively.

I, like most people, first encountered the periodic chart in high school. And I was unaware of any beauty behind the periodic chart or chemical theory. I was somewhat attracted to the mechanical aspects of the chemistry lab -- the glassware, the Bunsen burners -- and all the tangible aspects. But instead of focusing on experiments, I built elaborate rubber gas lines snaking under desks in order to "gas out" other students according to some WW I trench warfare reenactment going on in my head. Seriously, I don't remember much from high school chemistry. I may have learned the names of a few elements, but I was pretty much a smart ass in my first two years of high school and I paid a price for that. It probably didn't help that I had a terrible teacher who didn't know much chemistry himself (he was an earth science teacher). My high school had a regular chemistry teacher with a chemistry background (Mr. Z), but space was limited in his class and I didn't make the cut. The irony. But I digress. Getting back to the book: yes I too associated chemistry with dweebs. I fought the dweebs and the dweebs won. I became a dweeb or as we affectionately called ourselves in grad school "chem nerds."

Page 12, middle:

Before introducing the periodic table, every teacher should strip away all the clutter and have students just stare at the thing, blank.

Hey!  I made a similar point back here, except I proposed actually testing such knowledge.

The author is keen on stressing the rectilinear grid structure -- the Cartesian qualities. And for good reason: the chart is the form we all know -- but still, it is just a convention. There is nothing intrinsic about that flat tabular presentation.  I "co-invented" an alternative version here.

There is a rich history of how the grid was assembled. First came columns in the early 19th century: Döbereiner's triads --though the column metaphor presumes a vertical relation which didn't yet exist. Then came Newlands with his rows and notions of repeating layers. And then came Mendeleev who envisioned the whole thing well enough to predict where holes were for missing elements.

Page 13, last paragraph:

For each element, its geography is destiny. In fact, now that you have a sense of what the table looks like in outline, I can switch to a more useful metaphor: the periodic table as a map. And to sketch in a bit more detail, I'm going to plot this map from east to west, lingering over both well-known and out-of-the-way elements.

This reminded me of lecture I heard at the UW-Madison ca. 1982 given by a guest lecturer (I wasn't a grad student but rather a precocious undergrad). He put up a periodic table in which he likened it to a US map and showed how certain university research groups were working on the chemistry of elements in a "geographic" way: "Oh look, there's Jack Halpern in Chicago working on rhodium which sits in the "midwest"; and just north of him on the chart is Chuck Casey at Madison, working on iron; out west on the leftern edge is the Bercaw group exploring scandium; out east there's so and so." The modern periodic table is iconic.

Page 17, middle paragraph:

The repose of the noble gases is rare, however. One column to the west sits the most energetic and reactive gases on the periodic table, the halogens. And if you think of the table wrapping around like a Mercator map, so east meets west and column eighteen meets column one, even more violent elements appear on the western edge, the alkali metal. The pacifist noble gases are a demilitarized zone surrounded by unstable neighbors.

I love that. I made the identical point about the Mercator aspect back here (and this was before Kean published, WTF?). But none of this is original, so far...

...Doodle du jour:

What You May Have Missed

My modest blog just passed the quarter million views mark which is an inflated way of saying 250,063 pageviews. Thank you dear readers!

Here are the "top ten" posts according to my Blogger statistics, as well as a short recap:

1  The Parable Of The Doorkeeper*  19,420 views

This post is just my favorite Kafka parable and compares the German and English texts. It must be others' favorite too as it was Instalaunched (thank you, Professor Reynolds!)

2   Hail Britannic!  16,311 views

This one concerned the RMS Titanic's younger sister ship, HMHS Britannic and her sad story. Also, I drew a link between Jacques Cousteau's TV coverage of the shipwreck and the plot of James Cameron's Titanic. But I think many people were just looking for the interesting photo. 

3  Titanic Centennial: at the real Café Parisien  9,698 views

I think it odd that this post is number 3. It's just a famous old photograph of a very hip cafe on board the Titanic. Maybe that's all people were looking for. I did a series of posts on Titanic.

4  Forgotten Americans: Jack Thayer, Titanic Survivor  3,918 views

This post tells the story of young Jack Thayer and his heroic account of surviving the sinking. He was the first to publicly assert that Titanic broke in two. His views were contradicted in the official investigations and reports at the time, but he was vindicated when the wreck was actually found. Sadly, he committed suicide. 

5  The SS Great Eastern  3,452 views

Another famous ship and shipwreck story here. The photo is a haunting one and is worth a look. 

6  It's No Lye That Soap Is Made From Pot Ash  2,087 views

This post concerns the element potassium and was one of a series of posts I did covering the chemical elements. I got as far as rhodium with that series and plan to pick it up again with palladium.

7  Newlands' Law of Octaves 1,676 views

This post retells the interesting saga of John Newlands, the man who first drew attention to the chemical periodicity of the elements, a very favorite topic of mine. 

8  Last Letters From Stalingrad: #23  1,572 views

This post is one of a series of letters I transcribed from Last Letters From Stalingrad, an out-of-print, but very haunting book. See the links at the bottom of that post for more on that series. 

9  Last Letters From Stalingrad: #9  1,271 views


10  The Essence of Distillation 972 views

This is actually my personal favorite of the 10. If I could write more of these, I'd do it all day long. 

A New Periodic Paradigm

Before vanishing from the blogosphere, commenter Ritmo wrote back here:

I remember coming up with an improved periodic table while daydreaming during the inorganic chemistry course I took in college. When we were learning about d and f orbitals it occurred to me that a 2-dimensional table is flawed. Ultimately it should loop around as a cylinder, with the lanthanides and actinides poking out in a raised, textural format. For the life of me I can't remember how I worked it out in perfect detail, but it avoided the unnecessary breaks between groups I and II and reflected the fact that s and p orbitals underlie any expanded orbitals. Putting the transition metals smack dab in the middle of the non-metals and group II just didn't make any sense. And starting over again between the noble gases and group I instead of looping them around to the next orbital seemed an arbitrary convention, like hitting the return key or banging whatever that part was named on a typewriter as you finished a line and needed to move on to the next.

That is absolutely brilliant. It's like a revelation or a prophecy. It's not 100% original, but then few insights are. I will say more about that later. This revelation vexed me off and on for some time and I tried to sketch it until I realized that I needed to sit down like Richard Dreyfuss did in Close Encounters of the Third Kind and build the vision:

So sitting at the kitchen table, I started playing around with a flat periodic table, cutting it up and rearranging and I came up with this:

Cylindrical Periodic Table

Cylindrical Periodic Table

I'll be writing lots more on this in future posts. Lots more!

Chemical Gnomonclature*

Scotoma is the technical term for the blind spot in our field of vision. Our brains interpolate the missing data so we don't perceive a black spot, but in fact we have two scotomas, caused by the lack of retinal cells where the optic nerve joins the retina (see link).

The Periodic Table is a reticulated array of data. In the mid 1930's, element 43 was still conspicuously lacking. Dmitri Mendeleev, that great Russian seer of visions and father of the Periodic Table, foresaw its existence and called it eka-manganese, meaning "one-after-manganese." Here's what the family of transition metals looked like in the mid 1930's:

Chemists sought eka-manganese unsuccessfully for 75 years after Mendeleev's prediction: their efforts are nicely summarized by van der Krogt. Of the fruitless efforts, those of Noddack et al. came closest, and they proposed the name masurium in 1925. Several Periodic Tables from that era even included Ma beneath manganese.

Unequivocal proof for element 43 appeared in 1937, after an Italian team led by Emilio G. Segrè  isolated it from radioactive samples of next door molybdenum which had been bombarded with deuterium nuclei at Berkeley. They named the new element technetium from the Greek τεχνητος, meaning artificial.
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*Gnomonclature is an homage to James Joyce who invented a literary device called gnomon to accentuate character or story element.  In the words of his character Stephen in A Portrait of the Artist as a Young Man:

Absence is the highest form of presence.

The absence of eka-manganese drove generations of chemists to search for it because it was there--somewhere.

How the past gets Bury'd

I love stories like this one about the man who first noticed and explained what's behind my Rime of the Ancient Elements:

...an alternative proposal was put forth in 1921 by Charles Rugeley Bury (1890-1968), who was a lecturer at the University College of Wales at Aberystwyth. The scheme that he described succinctly in a mere seven pages is essentially the scheme to be found in modern introductory textbooks of chemistry and physics. He deduced from the chemical evidence that the electrons are arranged in successive layers containing 2, 8, 18, and 32 electrons. He gave a clear discussion of the electronic arrangements in the actinides and lanthanides, and even made some predictions (inevitably but not quite correct) for the transuranic elements.
Bury's scheme was reproduced in The Electronic Theory of Valency by Nevil Vincent Sidgwick (1873-1952); this was an important book that first appeared in 1927 and which interpreted the chemical behavior of the elements in terms of their electronic configurations. Sidgwick acknowledged the important contribution of Bury, but almost all subsequent accounts have failed to do so and Bury's name is now almost entirely forgotten.

~Keith J. Laidler, The World Of Physical Chemistry, Oxford University Press: New York, 1993

I can't even find a photo of Bury on the Internet. :(

The Rime of the Ancient Elements*

The discovery of krypton and the other noble gases ushered in a fuller understanding the elements, but it was still some time before the noble gases were depicted as shoring up the whole right-hand side of matter:

click to enlarge

The noble gases at the right-hand end appear to make the table rhyme like verse. The elements arranged in successive rows are like verses of length 2, 8, 18 and 32 elements (the gaps make this hard to see at first).
The natural rhyme of the Periodic Table is written in a 2n² meter, where n = 1, 2, 3, 4,.. . The atomic numbers of the inert gases show this remarkable regularity:

...2 elements...He[2]

...8 elements...Ne[10]

...8 elements...Ar [18]

...18 elements...Kr[36]

...18 elements...Xe{54]

...32 elements...Rn[86]

The ellipses show the number of elements between rhyming noble gas elements, 2, 8, 18, 32, corresponding to the natural meter, 2n², with n = 1, 2, 3, 4...

The Periodic Table is much more than rhyming noble gases; each element rhymes with the one above and the one below.  The whole damn thing rhymes.

__________________________

*Rhyme (rime) and rhythm were once distinctly different notions. The old word rime is a Germanic term originally meaning "series, sequence" as in the sequential ordering of the elements. link

More about the man who first noticed this here: Link

Gallium Arsenide is Germane to Solar Cells

Gallium arsenide, a simple combination of two elements, interconverts light and electricity; GaAs lasers turn electricity into light and GaAs solar panels convert light back into electricity. There are alternative combinations of elements for these tasks, but each has its limits. What strikes me is how gallium and arsenic bookend germanium:

I need a name for "binary combination of elements which brackets and mimics another element." The term isoelectronic is close but doesn't cut it for me. There is a mathematical symmetry about GaAs in view of Ge and it goes like this: (31 + 33)/2 = 32 or, in chemical logic symbols: (Ga + As)/2 = Ge.

Like gallium arsenide, germanium is a photovoltaic material. Google "germanium solar cell" and you will find cutting edge research involving blends of gallium arsenide with germanium. I'm glad there is on-going research into new materials because I am not sure we should be putting arsenic on every rooftop much like we're putting mercury in every lightbulb.

A similar "bookend relation" occurs a couple rows up in the Table between boron, carbon, and nitrogen. Look how boron and nitrogen bracket carbon:

Once again, (5 + 7)/2 = 6. And just like carbon, boron nitride (BN) has both graphite- and diamond-like structures. One type of BN is even harder than diamonds: link

I see a pattern here: the centrality of the carbon group, C, Si, Ge, etc. to the family of main group elements:

Doodle du jour

I doodled this today during a meeting (unrelated to this):

Click to enlarge

What am I getting at?

Conversations with Henry about another Henry

Henry: Henry Moseley really convinced everyone that atomic numbers were real. Atomic number was just Bohr's theory until Henry Moseley proved it true.

Me: Moseley's Law?

Henry: Yes. A theory becomes a law when it gets tested beyond disproof. He proved the atomic number using X-rays.

Me: How come Moseley never got the Nobel Prize like you did?

Henry: He was killed--took a Turkish bullet in the head at Gallipoli in 1915--the same year I was born.
 ___________________________
 

Henry Moseley (1887-1915)

At the link, Isaac Asimov is quoted: "In view of what he [Moseley] might still have accomplished ... his death might well have been the most costly single death of the War to mankind generally."

Behind the Metallic Curtain

An imaginary line runs down columns and across rows in the periodic table, dividing metals from non-metals:

The diagonal line can be thought of a boundary demarcating a section of elements equidistant from Fluorine, the epicenter of electronegativity:

Roughly, the "blue" elements closest to queen Fluorine (upper right) and fanning out across the territory up to and bordering the metallic curtain are non-metals; those beyond (yellow) are deemed metallic. But what makes a metal a metal and vice versa? What is the essence of "being metallic?"

Group 8 Love

The term "Group VIII Metals" refers to the 3 by 3 block of elements boxed in red below, especially in older texts. link  Note that they sit smack dab in the middle of the Periodic Table:

The 3 by 3 array is really three triads: first is the iron triad, comprising downwards iron, ruthenium, and osmium; the second triad is cobalt, rhodium, and iridium; the third triad is nickel, palladium, and platinum. So far in my series of posts about chemical elements, I've ignored the heavier metals, skimming sideways across the top of Group VIII, to get back to the right half of the Periodic Table. The metals below the blue line in the red box are called the platinum group metals: Ru, Rh, Pd, Os, Ir, and Pt. I will come back to them in due time. I know them the best of all the elements I've covered so far.

So why are they grouped together? First, they are usually found together (in nature), because they resemble each other chemically (though each element is of course distinct). Second, their electronegativities are similar to carbon's and to hydrogen's--this means that those main group elements tend to bond more covalently to the metals. Recall my point about the neutral ones--the covalent elements in the middle of a polarity continuum. Organotransition metal chemistry is largely (but not exclusively) the chemistry of those metals with hydrocarbons, hydrogen, and small organic molecules. The platinum group metals, especially rhodium, platinum, and palladium, are found for example in catalytic converters and fuel cells where they bring together disparate elements and catalyze their rearrangements.

One last thing. A lucky man discovered a process which still allows the modern day separation of the platinum group metals. He's the man who first gave metal wings.

Manganese Is Neither Transgendered Nor Racist

The words manganese and magnesium are related. Their entwined roots stem back to a place called Magnesia in ancient Greece where they were both found in abundance. Some speculate that Spartan swords were exceptionally hard because of manganese content in their iron. Manganese's word history is parsed here and van der Krogt has his take here.

Manganese has been used since antiquity both to color and to decolorize glass. The Venetians perfected "glassmaker's soap," making high art with it.  Glass always contains iron in trace amounts and this imparts a greenish "coke bottle" tinge. The addition of manganese to the molten glass produces a reddish-brown tinge which equalizes the absorption across the visible spectrum and gives so-called colorless glass. More reading on colored glass can be found here.

Manganese also demarcates an important trend in the Periodic Table. Moving from left to right across the first transition metal series, i.e., Sc -> Ti -> V -> Cr -> Mn, each element adds one more positive charge to its core (and one surrounding electron). Yet those electrons can be stripped by oxygen. A tipping point is reached between manganese and iron. Manganese is the last metal in that series to exhaustively lose all of its valence electrons to oxygen. Thus the manganese atom in permanganate MnO₄^-, is fully oxidized back to having an argon core. But moving just one element further to the right (to iron) is just enough change in electronegativity that iron retains two valence electrons: there is a ferrate but no perferrate.

Ironically, despite its reputation for rusting, iron retains an inner core of two valence electrons, even when completely surrounded by rapacious oxygen. Iron is one step closer to the noble metals.

Conversations with Henry

Henry:  I once gave an exam by passing out a blank Periodic Table and asked students to fill in the blanks from memory:

Me: Yikes! Did anybody pass?

Henry: A few. But everyone got vanadium right!

Transitioning To Real Metals

Look again at the "long form" of the Periodic Table:

click to enlarge

I've already blogged through three layers of the so-called main group elements, which are the two bluish colored blocks of elements bookending the reddish elements "inside." With reference to the very top left, calcium has the coordinates 4 down and 2 across. To get to the next element to the right, we have to jump the gap across the red rare earth metals and the underlying (and notorious) actinides to the first pink element, scandium.

Scandium is the first of the so-called transition metals, named from the Latin, transire = to go across or to cross over. The metaphor is that we're "crossing over" on our way back to the right-hand block of main group elements. Destination: krypton.

That's about all I want to say about scandium. But guess where it was discovered?  Yep. And by somebody named Lars even. Link

Choke On This!

The word pnictogen refers, in Greek, to the concept of suffocation. The Germans even call nitrogen Stickstoff, meaning suffocating stuff. I choke a little myself on the word pnictogen every time I hear it -- it comes out sounding like feeble erudition. The neighboring group words chalcogen and halogen are only slightly better, and the latter at least finds widespread use. But the concepts pnictogen, chalcogen, and halogen are cool enough and neatly correspond to the idea of periodic rhyming of elements.

Nitrogen is the group leader for team pnictogen and I have arrived at element 15, phosphorus, in my little Aufmarsch from element 1 to element 112 or so. Link

Anybody got any good phosphorus stories?

Conversations with Henry: Show Your Cards

[continued from here]

I discard two cards and pick up two more.

Me: What a shitty hand.

Henry: You gotta play what you're dealt.  Maybe we should play for money next time?

(I lay down my cards):

Me: I got iron, cobalt, and nickel!

Henry: Hmm! Not bad. A straight too. Too bad about the others. Maybe we should play hydrogen is wild next time.

(Henry lays down his cards):

Me: Shit Henry, that's a fullhouse: three noble metals and two noble gases!

Hard And Soft Elements: Size Does Matter

Here's a great Periodic Table showing the relative sizes of common ions. Cations are shown in red, anions are in blue.

Click To Enlarge

Cool things to note:

• Ions in the same column get bigger as one moves down a column.
• Look how ginormous cesium (bottom left) and iodide (bottom right) are.
• Look how small some ions are (Be²⁺ in particular).
• Look how invisibly small the proton is because H⁺ has no electrons. Hydride, H^-, having two electrons, is comparatively huge. It's almost like the planets Mercury and Jupiter. I wrote about Dr. Proton and Mr. Hydride back here.

A chemist named Ralph Pearson invented the concept of Hard Soft Acid Base (HSAB) Theory in the 1960s.  According to Pearson, "hard" (small) acids like Li⁺, Be²⁺, etc., naturally prefer binding with "hard" (small) bases like [OH]^- and O^2-.  Likewise, "soft" (larger) acids like silver, Ag⁺ and mercury, Hg²⁺ (when they aren't found in their elemental state) will invariably be found with a "soft" base, i.e., sulfide, S^2-.

So it goes.

Funny story about Pearson.  I saw him speak once at a special symposium dedicated to Henry. Pearson caught everyone's attention when he showed up late in the middle of a talk, entering at the rear, striding to the front of the room escorted arm-in-arm by two beautiful 20-something women (they turned out to be his grand nieces or something but everybody else was thinking "hired").  The women were dressed for cocktails too, not for a roomful of chemistry geeks. Pearson made his entry, said his hellos, and announced that he was just testing his principle of maximum hardness.

Conversations with Henry

Henry: Back in my day there were still holes and notches in the Periodic Table.
Henry sketched:

Me: But aren't the notches just from how we think about things?

Henry: Meaning?

Me: Meaning that the "notch" in the s- and p-blocks are because hydrogen and helium don't really belong to either block?

Henry: That's bullshit.  They certainly do belong with those other elements.

Me:  OK. So the notches come from discontinuities. Hydrogen and helium are completely s in character--and so are lithium and beryllium.

Henry: So why is helium parked over the p-block?

Me: Exactly! It really shouldn't be there.

Henry: Bullshit.  Helium is a noble gas. Of course it belongs there. Duh.
Henry looks at his cards and frowns.

Henry: I'll take two.
He discards two cards and I give him two more.