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.
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.
ReplyDeleteYou need to do the cliche free-association of this post with Metallica, Motorhead and other heavy metal bands.
Your alternative periodic table sound interesting. Here's a link showing some known alternatives: link.
ReplyDeleteI like the spiral version depicted here.
Thanks for the interesting links. I quickly perused them days ago but will check them out in more detail soon.
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