system
Given the following post, respond as if you're commenting on Reddit:
human
Why is Zinc more electrically conductive than nickel, and why is nickel more electrically conductive than iron?

I observed that in the 3rd shell of Zinc there are 18 (full), while in Nickel there are 16, and in iron there are 14.  Does this mean that the lower number of electrons in the 3rd shell = more electrical conductivity?
gpt
Electrical conductivity is a property of condensed matter, and it is influenced by a vast number of phenomena, much more than the amount of electrons surrounding a nucleus.

At the microscopic level metals are crystalline, the atoms are stacked orderedly in arrays (crystalline lattices) whose shape is determined by the symmetry class. Different materials may have different crystalline form.

What happens to the atomic orbitals, when you put several atoms close together regularly as in a crystal? 

In metals, the outer electron shells of the atoms overlap enough to give rise to composite "super-shells" called conduction bands. They are spatially de-localized (spanning the entire crystal) and are only partially filled with electrons, so that even a small electric field can give a bit of kinetic energy to the electrons in it, having them move.
 
Conversely, in insulators the outer electrons go into the valence band, completely filling it, while the conduction band is empty. There is a significant energy gap between the full valence and the empty conduction band and electrons cannot accept energy because they have "nowhere" to go, energetically speaking, being held back by Pauli exclusion principle. Only when the electric field is really strong they may jump from valence to conduction, this is the so-called "dielectric breakdown".

Back to electrical conductivity, different metals may contribute more or less electrons to the conduction band, the more the better.
But then you also have to think about what may disrupt conductivity:
 the electrons in the conduction band are able to "collide" with the imperfections of the crystalline lattice. The main ineliminable source of those crystalline defects is given by the thermal vibrations of nuclei around their rest sites: a nucleus being displaced amounts to a temporary electric charge that may attract or repel the electron, changing its momentum.

So, in general, electrical conductivity is a non-trivial phenomenon somewhat affected by atomic properties (the number of electrons in the outer shells), but principally determined by how the single atoms stick together (as a crystal) and by how the crystal properties, such as temperature, affect the dynamical behaviour of electrons in the conduction band.