What follows are ideas I have along with established concepts.
Valence Electron Shell
Electrons exist around a nucleus as standing waves. A standing wave is a stationary wave that’s created by traveling or moving waves which interact or interfere with each other constructively and destructively. Constructive interference results in traveling waves adding together, and destructive interference results in traveling waves cancelling out with each other. So, standing waves only actually exist at the locations where there’s constructive interference. These locations are called antinodes. The locations where there’s destructive interference and therefore where no standing wave exists are called nodes.
The reason an electron can only exist as a standing wave is due to the fact that since an electron has mass, it would lose energy and eventually crash into the nucleus due to centripetal acceleration if it actually orbited the nucleus. So, an electron particle actually just pops into and out of existence in a stationary manner throughout the territory of an antinode. Also, if an electron particle orbited the nucleus, then due to the extreme speed that it would have because of its kinetic energy and due to the extremely tiny territory that it occupies around a nucleus, it would have to orbit the nucleus quadrillions of times a second. In order for this noncircumferential and therefore noncentripetal electron movement to be maintained, there has to be a continual balance maintained where there’s a stalemate between all of the forces in the circumferential direction, which is actually what creates a standing wave. It’s when there’s not a balance like this that something moves in a net direction. A standing wave is the balance between the traveling waves which create it.
An electron standing wave is similar to how a chladni plate works. With a chladni plate, traveling waves deflect off its boundaries and interfere with each other, thereby creating a design of nodes and antinodes. An electron’s antinodes represent and correspond to its kinetic energy. The more kinetic energy an electron has, the larger its antinodes are, the larger the antinode amplitude, because a larger antinode allows for an electron particle to occupy more territory. This is as with when gas in a balloon is heated up, the gas particles push harder against the balloon’s walls and thereby push the balloon’s walls outwards. A larger antinode amplitude is equivalent to a particle form electron pushing away from the nucleus more due to its kinetic energy. The kinetic energy of an electron opposes its electrical attraction to the nucleus.
Electrons exist around an atom in layers where electrons in more interior layers are lower in kinetic energy. Only the outermost electron layer is involved with chemical reactions and therefore bonding between atoms. The electron layers are called shells, and each shell requires a certain number of electrons to occupy it in order to make it stable. The outermost electron shell is called the valence shell. All of the other electron shells are called the core shells. Only the noble gases have naturally full valence shells, which is why they’re so unreactive or inert. Chemical reactions occur due to the other elements seeking to have full valence shells like the noble gases.
When an atom doesn’t have a full valence shell, then that shell can’t align itself sufficiently with the first interior electron shell, the outermost core shell, in such a way that maximizes the valence shell’s access to the nucleus’ electric field and that minimizes the repulsions between the electrons of the valence shell and those of the first interior shell. A full valence shell allows the valence shell’s antinodes to fit in between the antinodes of the first interior shell thereby allowing the valence shell to get closer to the nucleus where its electric field is stronger. Also, when the valence shell’s antinodes are less directly over or above the antinodes of the first interior shell, then their access to the nucleus’ electric field is less blocked off by the outermost core shell’s antinodes being in the way. The antinodes of the interior or core shells blocking off the valence electrons from receiving access to the nucleus’ electric field is called electron shielding.
In addition to being more shielded, when the valence shell antinodes are more directly above or over the antinodes of the first interior shell, then the valence shell antinodes repel more with the antinodes of the first interior shell, resulting in the valence shell getting pushed further from the nucleus where the nucleus’s electric field is weaker. Because a more interior shell has a smaller radial distance from the nucleus, it’s more compact. This means that its particle form electrons are more densely concentrated or closer together. With a more exterior shell, because it has more kinetic energy, the density of its particle form electrons is less in the same way that with a more heated gas, the particles push against each other more and are therefore further apart from each other on average. So, when the valence shell pushes against the first interior shell, it loses and gets pushed outwards more while the first interior shell is hardly affected at all. The situation of more interior electron layers being more dense creates stability. This is because a more exterior layer can establish itself on the adjacent interior layer like a house on a foundation since the more dense and compact adjacent interior layer can bend the more exterior layer to its will.
There’s more space in the circumferential direction than in the radial direction, and the kinetic energy thrust of an electron standing wave is radial since it’s pushing against the nucleus and because it can’t move in the circumferential direction due to the risk of centripetal acceleration. So, when the antinodes of the valence shell are more directly above or over those of the first interior shell, then it’s encountering more of the first interior shell’s kinetic energy, and there’s also less space between the antinodes of the two shells. Because there’s more space in the circumferential direction, then there’s more space between the antinodes of the two shells when the antinodes of the valence shell more fit in between those of the first interior shell instead of being more directly above or over them. The reason that the core shells don’t participate in chemical reactions is because each of them has a full electron shell, and therefore they align with each other or fit together in an ideal manner that maximizes the access of each to the nucleus’ electric field and minimizes the repulsions between adjacent shells.
A way for an atom to get a full valence shell is through covalent bonding. A covalent bond is where two atoms share a pair of electrons. Bonding can only occur when electrons are associated with each other as pairs where the two electrons of a pair have opposite spins. Part of the reason that an unfilled valence shell is so unstable is because at least one of the electrons doesn’t have a spin pair partner while all of the other ones do. Because an electron spin pair acts like a single object, any lone electron constitutes an object with less mass which creates an imbalance when the valence electrons mutually repel each other within the valence shell.
That is, when the valence shell isn’t full, there’s a lack of uniformity within it. Because there’s uniformity within the first interior shell since it’s full, then the lopsidedness of the valence shell causes it to not be able to align with the first interior shell like it needs to, where the first interior shell would dictate the alignment due to its greater density and compactness. Instead, the lopsidedness of the valence shell causes it to just get pushed away by the first interior shell. The importance of electron distribution uniformity in an electron shell is indicated by the fact that with some atoms when the valence shell is half full, meaning that none of the electrons are spin paired, then the atom is very stable and unreactive. That is, there’s not an imbalance where there’s a mixture of spin pairs and lone electrons, but instead there are only lone electrons. So, when they repel each other in the electron shell, there’s uniformity of forces throughout the entire shell.
A transition metal atom isn’t able to get a full valence shell for itself. The best substitute or alternative that it has is being a part of a community of atoms in a metallic solid where the valence electrons are delocalized. That is, a valence electron isn’t restricted to a particular atom. In order to accommodate this, the atoms of a metallic solid pack closely together by fitting in between each other in order to minimize empty space. Basically, since a metal atom’s valence shell can’t have an alignment with the first interior shell that allows it to contract radially inwards in order to get closer to the nucleus, then the atoms of a metallic solid themselves contract radially inwards instead. This creates many more bond locations than exists with a nonmetal covalent bond structure. A metallic solid uses covalent bonds, but instead of a covalent bond being a mere component, a single antinode, of a single standing wave that completely surrounds an atomic nucleus as with a nonmetal situation, the covalent bond lobe of electron density is separate and independent. This is because the close packing acts like breakwater tetrapods which break up water waves. The close packing structure doesn’t allow for a single standing wave to be centered at a particular nucleus, but the problem in the first place was that an atom’s valence shell couldn’t get an arrangement that suited it where it was centered around a single nucleus. So, each covalent bond is an isolated antinode instead of being part of a larger standing wave. However, the metallic solid’s electron density still seeks to be uniformly distributed throughout the metallic solid in a manner similar to with a single standing wave. The close packing creates innumerable sealed off chambers, and each covalent bond is located at the perimeter or periphery of one of these.