Inside the Atom

Five parts opening the thing the last track deliberately left closed. It starts with the inventory — three kinds of particle in two places — and with two facts that do most of the later work: the nucleus holds nearly all the mass while taking up almost none of the room, so an atom is overwhelmingly empty and what feels solid is really electrons repelling electrons. The second part answers the question Track 2 asked twice and never settled, and answers it by elimination rather than assertion: electrons cannot decide which element an atom is, because a sodium ion has lost one and is still sodium; neutrons cannot, because chlorine comes with eighteen of them or twenty and both are chlorine; so it is the protons, and that number is fixed because no chemical process reaches the nucleus — which is also why the alchemists were attempting something chemistry cannot do. The third part clears up a number that looks impossible, since atoms are built from whole particles and yet chlorine is printed as 35.5; it is a weighted average of two isotopes, and no chlorine atom weighs it. The last two parts move outwards to the electrons and find the pattern that explains the periodic table: shells fill from the inside, only the outermost electrons are exposed to another atom, and so the elements repeat every eight. By the end the table is a consequence rather than a chart — rows are shells being filled, columns are outer electrons, and an element can be described from its position before anybody tests it.