One of the foremost scientists of the 20th century, the Nobel Prize winner Niels Bohr was the first to apply quantum theory to atomic structure. Bohr's studies became more and more theoretical in character. In doctor's dissertation Bohr explained the properties of the metals using the electron theory. It was in that he first tried to combine the electron theory with the Planck's quantum theory of radiation.
His intensive investigations into the radioactive phenomena resulted in the work on the absorption of alpha rays, which was published in 1912. Bohr’s first great work began with a study of the theoretical implications of the nuclear model of an atom proposed by Rutherford. In 1913 he combined the concept of the nuclear atom with the quantum theory of Max Plank and Albert Einstein. It was the revolution in classical physics. The main idea of his theory is shown in 3 postulates: -The electron can move near nucleus according to some stationary round level. -Staying at the stationary level an electron does not emit energy -There is emission when an electron has discrete transition to other stationary levels
But this theory was based on some contradictions. Bohr considered electron as a particle but not a wave. In 1922 Niels received the Nobel Prize for physics for his work on atomic structure and atomic emission.
Bohr worked during the winter of 1939-1940 at Princeton University, where he developed the theory of atomic fission that led directly to the first atomic bomb. He had conclusion, that the uranium 235 will be an atomic fuel.
Bohr constantly advised the authorities to use an atomic energy for peaceful aims and he made the report ‘Atomic Physics and Human Knowledge’. In 1957 he was the first to receive United States award “Atom for Peace”. Denmark Academy of Science established the gold medal where Bohr’s head and the phrase ‘Contrast is essence of complementary were drawn.
Niels Bohr died in Copenhagen in 1962, when his atomic theory was 50 years old. Bohr’s atomic theory is the greatest contribution to human knowledge that resulted in two modern sciences: the nuclear physics and the quantum physics.
These days they are engineering sciences and represent real huge industries. Besides Niels Bohr was a teacher of many talented scientists who received the Nobel Prize later.