Niels Bohr investigated the structure of the atom and won the Nobel Prize in Physics in 1922 for discovering the Bohr model. He developed the liquid drop model of the atomic nucleus, proposed the idea of complementarity and identified the U-235 isotope essential for nuclear fission. After fleeing the German invasion of Denmark, he worked on the development of the atomic bomb at Los Alamos in the United States.
The Bohr model proposes electrons orbit the nucleus because of electromagnetic forces rather than gravity. Because of this difference, electrons do not collapse into the nucleus but travel from one orbital shell to another as energy levels change.
As a Danish citizen, Bohr resisted involvement with German nuclear power research and aided many Jewish scientists in their escape from Nazi power. He fled Denmark in 1943 and eventually made his way to London, where he was involved with experiments for a viable nuclear fission bomb.
Bohr was adamant that atomic research should be shared, causing Winston Churchill to view him as a security risk. He organized the Atoms for Peace Conference in Geneva in 1955.
Bohr's son Aage Niels Bohr also contributed to the world of physics. Aage won the Nobel Prize in Physics in 1975.