The chemists have retained until today the obsolete prejudice that 0 is not a number equivalent with any other cardinal number.
Because of this, all published periodic tables are missing 1 chemical element.
Ignoring the artificial oganessian (of which it is not possible to make more than a few atoms that decay instantly), the column of the noble gases must have 7 noble gases that are encountered in nature: neutron (Z=0), helium (Z=2), neon (Z=10), argon (Z=18), krypton (Z=36), xenon (Z=54) and radon (Z=86).
Of these 7, the first and the last, i.e. neutron and radon are unstable and decay quickly, while the other 5 are stable.
Neutron does not enter in chemical combinations, but the same is true for the other light noble gases, helium and neon, so this does not make it distinct from the other chemical elements. Like also technetium and promethium, neutron is a chemical element that does not have any beta-stable isotope (because the beta-stable isobar with A=1 has Z=1, i.e. it is an isotope of hydrogen).
> the obsolete prejudice that 0 is not a number equivalent with any other cardinal number.
When adopting zero in that way, to be consistent you’d also have to consider “nothing” to be an isotope of neutron.
But the real answer is that chemical elements imply atoms, and atoms imply the combination of a nucleus and bound electrons. The neutron is considered a subatomic particle.
The same is true for hydrogen ionized once, helium ionized twice, lithium ionized thrice, and so on. From the point of view of chemistry, a neutron is not more subatomic than a hydrogen nucleus or any other nucleus. There is indeed a difference between the nuclei with A = 1 and the nuclei with A > 1, because the latter can be decomposed into the former at high enough temperatures, of a few tens of MeV, similarly to the decomposition of any multi-atomic molecule at high enough temperatures.
"Nothing" is not an isotope of neutron, for the same reason why it is not an isotope of sulfur or of iron, i.e. the mass number A is defined as a positive integer number and there is no reason to define it otherwise. On the other hand, the atomic number Z can be defined as an integer number if antimatter is also considered, or as a non-negative integer when applicable only to ordinary matter.
Considering neutron as a noble gas like the others simplifies certain descriptions by eliminating special cases that must be considered separately.
The noble gases can usually be ignored in chemistry, because they typically do not participate in chemical reactions, but in nuclear reactions there is nothing special about them, so the noble gases, including the neutron, participate in nuclear reactions like any other elements.
Because of this, all published periodic tables are missing 1 chemical element.
Ignoring the artificial oganessian (of which it is not possible to make more than a few atoms that decay instantly), the column of the noble gases must have 7 noble gases that are encountered in nature: neutron (Z=0), helium (Z=2), neon (Z=10), argon (Z=18), krypton (Z=36), xenon (Z=54) and radon (Z=86).
Of these 7, the first and the last, i.e. neutron and radon are unstable and decay quickly, while the other 5 are stable.
Neutron does not enter in chemical combinations, but the same is true for the other light noble gases, helium and neon, so this does not make it distinct from the other chemical elements. Like also technetium and promethium, neutron is a chemical element that does not have any beta-stable isotope (because the beta-stable isobar with A=1 has Z=1, i.e. it is an isotope of hydrogen).