A partial toy band keeps both filled and empty slots 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
A partial band has some filled slots
Five electrons fill 5 of the 8 slots.
filled=electrons=5,slots=8
The empty count closes the ledger
The remaining empty count is 3, so the occupancy verdict is partial.