According to Salvatore Califano in his book, Pathways To Modern Chemical Physics, one of the first philosophers to credit electricity with holding together Matter was a man named Aepinus. Aepinus theorized in the 1750s that electrical “fluid”– the very substance of electricity– was made-up of very small (our authors say that he described them as”immaterial”) particles. Aepinus believed (just on a hunch really), that Matter containing alot of these electric particles would attract Matter containing very little. Conversely, he felt that two pieces of Matter both containing alot of electric particles would repel each other.
Thus, it is evident that as far back as the mid-1700s: 1) Electricity was already being associated with miniscule particles of matter, and that 2) Electricity was already being credited with attracting substances to each other.
That’s about as far as theoretical physics gets on the matter for the next hundred years. Then, in the middle of the 1800s, vacuum tubes truly worthy of the name began to be created. The importance of vacuum tubes for science and for modern life can hardly be overstated. In fact, I’m tempted to do a post just on these babies. Regardless, in 1855 Henrich Geissler was producing some sweet, evacuated tubes. Julius Plucker took one of Geissler’s improved models and slapped an electrode into each end of it and threw the switch to see what would happen. What he discovered was that a greenish luminescence appeared in the tube. His student, Hittorf, labeled this glowing lights “Cathode Rays.” Hittorf said that Cathode Rays were what electricity looked like when it passed through a vacuum.
For years, any farther insight into the nature of Cathode Rays remained allusive– although Plucker did notice that Cathode Rays responded to the influence of a magnet. In 1879, William Crookes, after playing with Cathode Rays and magnets for awhile, found that Cathode Rays were repelled by the negative pole of a magnet, and deduced that the Rays carried a negative charge. The suggestion by George Johnstone Stoney that the name “Electron” be settled-upon to designated these proposed Cathode Ray particles was almost immediately accepted, and the world’s first known elementary particle was christened.
So, as we see, by the early 1880s, scientists are working toward the notion that Electricity is composed of tiny particles carrying a negative charge.
Near the end of the 1800s, J.J. Thomson was studying Cathode Rays by subjecting them to electric and magnetic fields. Studying the pattern of path deviations he produced by varying these fields, he came-up with what he believed to be a good approximation of the ratio between the conjectured Electron’s mass and the amount of charge it carried. Thomson proposed that both the mass and the charge of the Electron are invariable– in other words… every single Electron in the Universe is identical– [I find this hard to believe in a Universe of such variety]… The mass of the Electron Thomson set to equal about one-one-thousandth’s the mass of the smallest known element, the Hydrogen atom, and he assigned the Electron a quantum of negative charge in terms of its mass.
In 1899, R.W.H. Abegg, echoing the theory of Aepinus from nearly a hundred and fifty years earlier, proposed that Matter was held together by the interactions of Electrons. Although, as far as I can tell, Abegg’s theory of atomic binding, like the theory of Aepinus, did NOT necessitate that Electron energy be “negative.”
By 1904, attempting to explain why the Electrons of Noble Gases are so disinclined to interact with other atoms, Abegg proposed that the pattern of Electrons in a Noble Gas is in someway (?) complete, and therefore, the atom does not crave electric interaction with other atoms. He conjectured that an atom (let’s call it Atom A) which is NOT a Noble Gas possesses an incomplete Electronic configuration, and so it WILL crave interaction with other atoms– but only those atoms (or sets of atoms) whose own Electronic configurations will complete the configuration of Atom A by virtue of the interaction of the atoms involved. Abegg imagined Electrons as occupying different circular zones, or shells, in the atom, and that the internal shells are all sated when it comes to Electricity needs… It is only the outermost shell which — except for the Nobel Gases– feel incomplete.
The “incompleteness,” whatever it is, of Electronic configurations in non-Noble-Gases has nothing directly to do with a charge imbalance– indeed, many if not most atoms, whether they long to acquire or dump Electrons to feel complete, are perfectly charge-balanced already. I am unclear as to what the fundametnal nature of the “incompleteness” is. I assume it’s some sort of Energy level thing, but I don’t think it can be related to “stability” since most non-Noble atoms– even when highly reactive– are just as “stable” as Nobles.
In 1913, Kossell (an associate of Abegg) described in more detail the nature of the inner shells of atoms, declaring that the internal shells of an particular non-Noble atom is, in terms of the number and configuration of Electrons, equivalent to the Nobel Gas closest behind it on the Periodic Table. For Kossell, all atoms were attempting to “complete” an outermost shell which would bestow upon the atom a Noble-Gas-like fulfillment. To produce this desired state, some atoms would gladly give-away electrons so that they could become the Noble Gas within (electronically speaking), and other atoms would find it more desirable to acquire one or more electrons and take on the “complete” outshell structure of the next Noble Gas on the Table.
However, going back to what I said earlier about the “incompleteness” having nothing directly to do with atomic charge-balance, when these Noble-Gas-wanna-be’s add or subtract Electrons, the charge-balance of the atom goes awry, and the atom becomes an Ion– that is, it acquires a net charge, either positive (if an electron is jettisoned) or negative (if an electron is snatched).
However, there is another option available to the unhappy atom, and that is to join with another atom seeking the opposite of what it is seeking. By this I mean that an atom wanting to shed an Electron can join an atom wanting to give away an Electron, or an atom wishing to gain an Electron can fuse with one wanting to lose one. This Electrical interaction of opposites (and again, we hear the echo of Aepinus from a century and a half earlier) is called an Ionic Bond. This was how Kossell imagined atoms bonded together to make molecules.
But a problem with this theory was, well… reality. It was widely known that two Oxygen atoms or to Nitrogen atoms would bond together. That seems to contradict the idea that atoms want to bond only with atoms of opposite Electronic needs.
Enter Gilbert Lewis. Lewis conjuctures that atoms sometimes “share” Electrons, in what is known today as a “Covalent” Bond. Under Lewis’s covalent bond, two atoms both preferring to obtain another Electron could borrow each other’s, thus “completing” the outer shell of each atom.
Later in the 20th century, when scientists discovered that bonding angles between atoms in molecules did not match up with the Electron “orbits” which physicists had, in the recent decades, so painstakingly bestowed upon the atomic world, Pauling came up with the idea of “Hybrid Orbits.” Pauling said that Hybrid Orbits formed due to the reconfiguration of Electronic energies during the act of bonding. For one thing, the Electrons– all sharing a like charge– will want to be as far apart from each other as possible, and these mutual repulsions will effect bond-angles.
In another problem with the Electronic Theory of bonding, it was discovered that some atoms were bonding together which had no business doing so. These atoms, according to the theories, did not possess enough outershell Electrons to make the witnessed bonds. Upon these occassions, Mulliken conjectured that internal Electrons were being “promoted” to the outermost shell, where they could then participate in the bonding love.
Personally, I’m still not convinced that physicists have fully explained WHY Electrons, which should repel each other, are nevertheless the main agents molecule-building.
Furthermore, there is still loads of cognitive dissonance present when it comes to thinking about Electrons and bonds. The major weirdness is that, after Born’s ideas, as our authors say… “the Electron completely lost its identity as a particle and became a cloud of negative charge.” And yet, atomic interactions are still largely contemplated– and taught in schools– as if they are the result of miniscule negative particles being snatched, donated, or shared.
The Electron can also be credited with causing scientists to go in search of Matter possessing a POSITIVE charge. As our authors tell us, once it was suggested that some pieces of Matter possess a negative charge, the idea that there must be balancing positive charges was not long in coming– especially since our world appears to be largely charge-neutral.
And indeed, at about the same time J.J. Thomson was assigning mass and charge values to the conjectured Electron, Eugen Goldstein and Wilhelm Wien, working separately, were toying around with something called “Canal Rays,” which they found to respond to a magnet in a fashion opposite to that of Electrons–meaning that Canal Rays were deflected away from the positive pole of a magnet. Therefore, both men said that Canal Rays were made-up of tiny positively charged particles. Additionally, in 1898, Wien stated that Canal-Ray-particles were about the same size as Hydrogen atoms– in other words, about a thousand times bigger than Electrons. Later, these postively charged particles will be termed “Protons,” and they will be found (coincidentally? suspiciously?) to possess the same amount of charge (though positive for the Proton) as the much, much smaller Electron.
These purported discoveries of positive charges in atoms, and their resultant explanatory theories, started a multi-decade cascade of conjectures about how atoms are put together… leading eventually to the crazy “quantum zoo” of particles many physicists today honestly believe to exist.