Niels Bohr was born on in Copenhagen, Denmark. He won the 1922 Nobel Prize for physics, chiefly for his work on atomic structure.

In 1913, Bohr published a theory about the structure of the atom based on an earlier theory of Rutherford's. Rutherford had shown that the atom consisted of a positively charged nucleus, with negatively charged electrons in orbit around it. Bohr expanded upon this theory by proposing that electrons travel only in certain successively larger orbits. He suggested that the outer orbits could hold more electrons than the inner ones, and that these outer orbits determine the atom's chemical properties.

Bohr also described the way atoms emit radiation by suggesting that when an electron jumps from an outer orbit to an inner one, that it emits light. Later other physicists expanded his theory into quantum mechanics. This theory explains the structure and actions of complex atoms.

Bohr became a professor of physics at the University of Copenhagen in 1916. In 1920, he was named director of the newly constructed Institute of Theoretical Physics at the University. Bohr became a Fellow of the Royal Society of London in 1926, receiving the Royal Society Copley Medal in 1938.