Empty, partial, and filled rows keep slot accounting visible. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Zero electrons is the empty boundary row
The band has 4 sites times 2 states per site, so total slots are 8. Electron count 0 gives filled slots 0 and empty slots 8.
slots=4⋅2=8,filled=0,empty=8
Five electrons leave destination slots
The band has 4 sites times 2 states per site, so total slots are 8. Electron count 5 gives filled slots 5 and empty slots 3.
slots=4⋅2=8,filled=5,empty=3
Eight electrons fill every toy slot
The band has 4 sites times 2 states per site, so total slots are 8. Electron count 8 gives filled slots 8 and empty slots 0.