There were many contributors to the structure and known atributes of the modern atom; one of these such contributors, and arguably the most important, is Niels Bohr. Niels Bohr was a physicist born October 7th, 1885 in Copenhagen, Denmark and studied under the tutelage of several other auspicious atomic scientists of the time such as Ernest Rutherford and J.J. Thompson. After World War II broke out in Europe, Bohr left his distinguished teaching position at the University of Copenhagen to flee to the United States to continue his research. During his hiatus in America, Bohr became actively involved in the Manhattan Project which was a collaboration of scientists commited to discover the process behind splitting the atom and unleashing nuclear energy. However, his contributions were not limited to the development of advanced weaponry for the United States of America; no, what Bohr is probably most notorious for is his development of atomic structure, creation of the Bohr model, and the discovery of quantum mechanics.
After his work with J.J. Thompson, who discouraged his innovative ideas, Bohr began working closely with renowned scientist Ernest Rutherford. Instead of acting as a retardant for the bright flame of ideas that Bohr provided, Rutherford encouraged his work and indeed even furthered his efforts to reform current beliefs in regards to the structure of the atom. Bohr postulated that, instead of a random sequence of travel, electrons moved around the nucleus in a fixed orbit, not unlike how the planetary bodies located in our very solar system orbit around the sun. Bohr also theorized that, instead of a dense cloud with a random spattering of practically weightless electrongs, these electorns actually followed a quite organized path and, as they continue along thier infinite sequences, they either emit or consume energy. He was also of the opinon that, as these electrons traveled form one orbital sphere to another, they emanate miniscule amounts of radiation. In was this occurance, he speculated, that helped distinguish each individual atom's chemical and physical properties.
In conjunction with his modifications to the atomic struction, Bohr came out with a new representation of the atom to replace his old mentor J.J. Thompson's "plum pudding" model. This new portrayal, called the Bohr model (depicted in figure 1) contained a centeral nucleus that consisted of an assortment of both protons and neutrons. Surrounding the nucleus is several rings or orbital paths that the negatively charged electrons must follow; as the paths grow farther and farther away from the innermost location, so does the number of traveling electrons grow exponentially. For example, the first "shell" of the atom can hold up to two electrons; the second can hold six, the third holds ten, and so on. This model was intrumental in helping scientists diffuse the mysteries associated with the atom as well as debunking popular atomic myths of the time.
Lastly, Niels Bohr made monumental leaps in the fields of theoretical physics through the discovery of quantum mechanics. Nicknamed "The Father of Quantum Theory", Niels Bohr certainly lived up to his title by clarifying several of the most prominent dilemmas faced when dealing with quantum physics. He crafted the concept of complimentarity which brings into light two seperate postulates: 1) that the atomic system can only achieve stability in a specific set of stationary states and that only a change in energy can traverse the atomic system from one state to another and 2) the possibility that the atom may be able to take in and release levels of radiation equal to the difference found between the two states. Bohr used these two hypotheses in order to make improvements to the already existing Bohr model as well as to create a reasonably accurate description of all the known basic chemical elements. After his contributions to the American Atomic Energy Project, and the ensuing problems occuring in conjunction with atomic weaponry, Bohr sought to use the atom and quantum mechanics to peacefully solve the problems of the world and advocated open relationships between the countries of the world.
Niels Bohr died on November 18th, 1962 in his hometown of Copenhagen, Denmark. He was an inspirational figure in the fields of atomic science, biology, and theoretical physics and greatly increased mankind's understanding of how this world functions through his structuring of the atom, creation of the Bohr model, and advancements in quantum mechanics. His acomplishments will forever be revered for the way his assisted in the progression and evolution of humanity and science.