Monday, 8 February 2016

Happy birthday to a man who got things astonishingly right

It was good of Google to remind us, in one of its doodles, that 8 February was Dmitri Mendeleev’s birthday (the 182nd, as it happens, but then Google makes a bit of a point of celebrating slightly odd anniversaries).

What I’ve always liked about Mendeleev is that he didn’t just build the periodic table, which we’ve no doubt all gazed at in long boring moments if we’ve ever had chemistry classes, he used it to do something I regard as absolutely central to the nature of the scientific method as it emerged in the eighteenth century. For a long time, scientists set themselves the goal of explaining the phenomena they observed. They watched bodies falling at the Earth’s surface, for instance, and they came up with notions of rapidly spinning vortices of ethereal (weightless) matter that drove objects downwards, and lots of people went along with the idea because it seemed quite plausible.

Attractive as well as useful
And note number 32
The problem is that this view of the world suggests that objects would also be pushed sideways by the spinning matter, and they clearly aren’t.

The beauty of Newton’s theory of gravitation, long resisted by the proponents of the vortices, was that it predicted things that actually happened, from the movement of the planets (or most of them, anyway – Mercury needed Einstein to come along), to the orbit of the moon, to the action of the tides, to the falling of bodies, all in one theoretical framework. It’s that predictive rather than simply explanatory capacity that gave Newton’s arguments such force, compared to his adversaries.

Mendeleev did the same, perhaps even more forcefully. He built his periodic table, and discovered there were holes in it: squares that ought to contain the name of an element, but for which none was known.

For instance, he worked on group 14 of the table, which starts with one of the most important elements of all, for us, since it’s the basis for all life: Carbon. It has the capacity of forming long chains of carbons atoms, or alternatively carbon rings, and they are vital in supporting life.

The next element is Silicon, which appears, in particular, in sand and glass.

Then there was a gap. Because the next know element in Mendeleev’s time was tin. It’s so much bigger than Silicon that there had to be another element in between them. Besides, tin is a metal, as is the then last-known element of the group, lead, whereas carbon is definitely non-metallic and silicon only slightly less so; there had to be some transitional element between them.

In 1869, Mendeleev predicted that the material would have an atomic weight of 72, be grey in colour, with a density of 5.5 grams per cubic centimetre and a high melting point. Its chloride, he believed, would boil at a temperature below 100C, and would have a density of 1.9 gm/cc.

In 1886, the element Germanium was discovered. It has an atomic weight of 72.61. It’s grey with a density of 5.35 g/cc; its melting point is 947 C; its chloride boils at 86C and its density is, indeed, 1.9.

Germanium also happens to be a semi-conductor, which makes it important in transistors, and places it neatly in a transition between non-metals and metals.

That’s what I call predictive capacity: to say so much about something unknown, and to find confirmation that close when it’s discovered. Impressive stuff. And truly the stuff of science.

So happy 182nd, Dmitri. And thanks for that great table. It whiled away many a boring period in chemistry lessons.

Impressive man. And didn’t he look it?


Awoogamuffin said...

Yes and I also enjoy the story of the tension between Mendeleev and Paul Emile Lecoq de Boisbaudran regarding the properties of Gallium, which Mendeleev also won.

But it should be noted Mendeleev got a lot of things wrong. Sam Keen talks about them in the disappearing spoon, but I remember one of them was that he predicted an entire periodic table on the other side of hydrogen. Just goes to show that the power of predictive reasoning does need the experimental data to back it up in the end.

David Beeson said...

Good points. But I suppose it shows the validity of the scientific method: it's the confirmation of predictions that makes the point.

Lakshman said...

A Person can merely enjoy two occasions relating to him/her personally.
One, is Birthday - a day in a year.
Another, is Marriage Day - A Day in a Lifetime.
Both are most precious ones, which stay memorable for a long time.

I wish you a very very Happy Birthday to you.

Birthday Wishes said...

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