Parkinson's law He also wrote the book "Mrs. Parkinson's Law: and Other Studies in Domestic Science". Parkinson's law Parkinson's law is the adage that "work expands so as to fill the time available for its completion". It is sometimes applied to the growth of bureaucracy in an organization. This law is likely derived from ideal gas law, whereby a gas expands to fit the volume allotted. Articulated by Cyril Northcote Parkinson as part of the first sentence of an essay published in "The Economist" in 1955 and since republished online, it was reprinted with other essays in the book "Parkinson's Law: The
Aufbau principle building-up principle or the aufbau rule. The details of this "building-up" tendency are described mathematically by atomic orbital functions. Electron behavior is elaborated by other principles of atomic physics, such as Hund's rule and the Pauli exclusion principle. Hund's rule asserts that even if multiple orbitals of the same energy are available, electrons fill unoccupied orbitals first, before reusing orbitals occupied by other electrons. But, according to the Pauli exclusion principle, in order for electrons to occupy the same orbital, they must have different spins (−1/2 and 1/2). As we pass from one element to another of next higher atomic