Erwin Madelung was a German

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 physicist.

He was born in 1881 in Bonn

Bonn

Bonn is the 19th largest city in Germany. Located in the Cologne/Bonn Region, about 25 kilometres south of Cologne on the river Rhine in the State of North Rhine-Westphalia, it was the capital of West Germany from 1949 to 1990 and the official seat of government of united Germany from 1990 to 1999....

. His father was the surgeon Otto Wilhelm Madelung

Otto Wilhelm Madelung

Otto Wilhelm Madelung was a German surgeon who was a native of Gotha.In 1869 he received his medical doctorate from the University of Tübingen, and later worked in a military hospital during the Franco-Prussian War...

. He earned a doctorate in 1905 from the University of Göttingen, specializing in crystal structure

Crystal structure

In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...

, and eventually became a professor. It was during this time he developed the Madelung constant

Madelung constant

The Madelung constant is used in determining the electrostatic potential of a single ion in a crystal by approximating the ions by point charges. It is named after Erwin Madelung, a German physicist....

, which characterizes the net electrostatic effects of all ion

Ion

An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s in a crystal lattice, and is used to determine the energy

Energy

In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

 of one ion.

In 1921 he was appointed head of theoretical physics at the University of Frankfurt/Main, which he held until 1949. He specialized in atomic physics

Atomic physics

Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. It is primarily concerned with the arrangement of electrons around the nucleus and...

 and quantum mechanics

Quantum mechanics

Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...

, and it was during this time he developed the Madelung equations

Madelung equations

The Madelung equations are Erwin Madelung's alternative formulation of the Schrödinger equation.-Equations:The Madelung equations are quantum Euler equations:\partial_t \rho+\nabla\cdot=0,...

, an alternative form of the Schrödinger equation

Schrödinger equation

The Schrödinger equation was formulated in 1926 by Austrian physicist Erwin Schrödinger. Used in physics , it is an equation that describes how the quantum state of a physical system changes in time....

.

He is also known for the Madelung rule, which states that atomic orbitals are filled in order of increasing n + l quantum numbers.