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The Bohr Atomic Model - a quantum approach
In Bohr's theory of the atom, he expanded upon and critiqued the then accepted and current Rutherford Model, in which electron's orbits were considered unstable. This, however, was an unexplainable phenomenon because of the inherent stability of atoms, the smallest characterizable unit of matter. Through previous discoveries at the quantum level, Bohr derived a formula that defined electrons' orbits as possessing both a finite size and energy (Bohr Atomic Model). -
Bohr's Atomic model continued
From Bohr's theory of fixed electrons' orbit size and energy, he was able to identify quantum-jumps that electrons make while in orbit of the positively-charged nucleus, in which they either transfer energy, in the form of photons (electromagnetic radiation) by either emitting or absorbing it. This would serve as a fundamental model in the field of quantum physics, that is still used and accepted today (at a conceptual level) (Bohr Atomic Model). -
The Complementary Principle - and the birth of Quantum Mechanics
Bohr's Complementarity Principle was paradoxical (hence why the dual properties of matter and light went misunderstood for so long), because, although matter and light exhibit both of these properties simultaneously, they can not be measured simultaneously. This, eventually, would lead to the Copenhagen Interpretation (Harrison). -
The Copenhagen Interpretation
The Copenhagen Interpretation is a fundamental theory that helped to formulate the groundwork of quantum mechanics. It states that systems at the atomic and subatomic level, say, an electron of an atom, do not possess any definite properties until measured. Meaning, systems at an atomic level hold no definite pathways or positions in space. For example, an observer of an electron can not know the position of an electron until it is measured (Harrison). -
The Copenhagen Interpretation continued
And, this observation of the electron, or any system at the atomic level, is only observed as such, because the electron is forced to choose a pathway once measured. Hence, resulting in the probabilistic nature of phenomena at the quantum level. That is, you can never precisely know the position of a quantum entity, only where it is more likely to be than not (Harrison). -
The Complementarity Principle
Due to conflicting phenomena that could not be explained solely with classical physics (because of evident discrepancies that were experimentally observed between particles at the macro- and micro-level), Bohr sought a method to explain them. This led to what is known as the Principle of Complementarity, which states that all matter (and energy, including light) exhibit wave-particle duality, in which matter and energy exhibit both characteristics of a particle and that of a wave, simultaneously -
Summary
Bohr's ideals, which were based off of preceding physicists' works, such as that of Max Planck's, was instrumental in laying the groundwork for quantum mechanics, a new theory of how particles behave on a microscopic level. Bohr helped to pave the way to a new paradigm in physics. And today, these ideas are still used and implemented in the study of quantum mechanics, as well as developing a relatively recent theory--String Theory (still in its infancy). -
References
"Bohr Atomic Model". Abyss.Uoregon.Edu, n.d., http://abyss.uoregon.edu/~js/glossary/bohr_atom.html. Harrison, David. "Complementary & The Copenhagen Interpretation". Faraday.Physics.Utoronto.Ca, 2000, https://faraday.physics.utoronto.ca/GeneralInterest/Harrison/Complementarity/CompCopen.html. Williams, Matt. "What Is Bohr's Atomic Model? - Universe Today". Universe Today, 2016, https://www.universetoday.com/46886/bohrs-atomic-model/.