Periodic Table for Chemistry?

The Periodic Table PT is viewed to be the iconic backbone of chemistry as the science of molecules formed by atoms (as physics) by chemical bonding determined by electron configurations or electronic orbitals. 

PT organises atoms into a rectangular scheme according to atomic numbers and s, p, d and f electronic orbitals as spherical harmonics in a shell structure with outermost shell containing valence electrons available for bonding. The valence electrons fundamentally reorganise from atomic orbitals to molecular orbitals during bonding into molecules. This is what textbook Standard Quantum Mechanics StdQM says.

PT thus has focus on atomic orbitals, but is used for molecular orbitals, which is a mismatch. A chemist would need a PT for molecules rather than atoms, but there is no such table. It thus seems that the physics of StdQM does not deliver so much to chemists, who have to form their own concepts of chemical bonding. 

In any case, the valence shell is central with s and p orbitals of two atoms combining to $\sigma$ bonds between s orbitals and $\pi$ bonds between p orbitals, but the picture seems very confusing to a non-specialist like me.  

RealQM is an alternative to StdQM based on non-overlapping one-electron charge densities with a direct real physical meaning, which appears to have the potential to deliver to chemistry. 

As a basic example, the H2 molecule is formed as two H atoms approach with their two electrons being represented by non-overlapping charge densities meeting at a separating plane orthogonal to the axis between kernels with continuity of non-zero charge densities. This allows concentration of charge densities between the kernels without cost of kinetic energy and so with total energy decrease compared to well separated kernels achieving bonding. 

In general the valence shell is divided into non-overlapping charge densities with maximum of 8 electrons which can be divided into subshells as 4+4, 4+3, 4+2 with different bonding. 

RealQM describes both atoms and molecules as the result of electron packing towards minimal energy in dynamic processes, in particular beyond reach for very dense packing with unphysical too small energy. So is the Lithium atom formed by 2 electrons dividing a 1st shell in two halves and the 3rd electron can only fill a 2nd shell, not penetrate into the 1st (because it is too big).

You find many examples of atoms and a limited collection of molecules here. It is possible that RealQM can form the PT for chemistry, which was not delivered by StdQM. RealQM connects to DFT and AiM but has a new Aufbau principle. 

Comment by chatGPT

Here’s a commentary on the post by the author of “Periodic Table for Chemistry?” on the blog of Claes Johnson. I highlight what I think works, what merits caution — and what the broader consensus in chemistry and physics suggests.

✅ What the post gets right / raises interesting points

• The post correctly observes that the Periodic Table (PT) is built around atomic (not molecular) structure: elements arranged by atomic number and electron-shell/orbital structure (s, p, d, f) — i.e. the periodic table is fundamentally a map of atomic electronic structure. claesjohnson.blogspot.com+2Encyclopedia Britannica+2

• It is true that when atoms bond to form molecules, the simple atomic-orbital picture “reshuffles” into molecular orbitals or more chemically complex bonding schemes. This complicates the idea that the PT alone suffices to understand molecular behavior. The post therefore raises a genuine conceptual tension: a “periodic table for molecules” could in principle be more directly useful to chemists.

• The article’s critique implicitly echoes a known reality: although the PT is enormously powerful, it is not a “complete theory of chemical bonding or molecular behavior.” Chemists routinely supplement it with quantum chemistry, molecular orbital theory, hybridization, empirical data, etc. As noted by standard expositions, the PT is a starting point for understanding periodic trends (valence, electronegativity, bonding tendencies), but chemistry always requires additional models. asbmb.org+2American Chemical Society+2

⚠️ Where the post ventures into speculation or controversial reinterpretation

• The post introduces an alternative framework, dubbed Real Quantum Mechanics (RealQM), in which atoms and molecules are described as “non-overlapping one-electron charge densities” rather than conventional delocalized wavefunctions, and suggests this could yield a “Periodic Table for chemistry” (i.e. more chemically relevant table than the atomic PT). That is a speculative and nonstandard proposal. The mainstream quantum mechanical description — using wavefunctions, orbitals and the full machinery of quantum chemistry — remains overwhelmingly successful in describing atomic, molecular, and material behavior.

• The post seems to argue that relying on atomic orbitals (PT’s foundation) to infer molecular bonding (molecular orbitals etc.) is a “mismatch.” While there is some philosophical merit to pointing out the conceptual leap from atoms → molecules, modern quantum chemistry precisely builds on the atomic basis to construct accurate molecular descriptions. The success of quantum chemistry in predicting molecular geometries, spectra, reaction pathways, etc., indicates that the “mismatch” is not fatal.

• The suggestion that chemists “need a periodic table for molecules” — while imaginative — may not be practically feasible. Molecules are vastly more diverse than atoms; a “table” summarizing all possible molecules with useful predictive power would be extremely complex, perhaps less useful than existing computational models, databases, and quantum-chemical methods.