Niels Bohr

Niels Bohr completely transformed our view of the atom and of the world. Realizing that classical physics fails catastrophically when things are atom-sized or smaller, he remodeled the atom so electrons occupied ‘allowed’ orbits around the nucleus while all other orbits were forbidden. In doing so he founded quantum mechanics.

Later, as a leading architect of the Copenhagen interpretation of quantum mechanics, he helped to reshape our understanding of how nature operates at the atomic scale.

Bohr knew Rutherford’s picture of the atom disagreed with the laws of classical physics. These said that negatively charged electrons must radiate energy and be pulled into the positively charged nucleus. Even when he wrote his Ph.D. thesis, Bohr stated that it was impossible for classical physics to explain behavior at the atomic scale.

Now he looked to the new quantum physics of Max Planck and Albert Einstein for a solution to the apparently impossible behavior of electrons. In fact, he started on this track in Manchester in 1912.

Quantum physics had established that when an object radiates heat or light waves, the emission comes not in a continuous stream, but rather in distinct packets of wave energy.

Einstein called these distinct packets photons. Like all waves, photons have a speed, frequency, and a wavelength.

Planck deduced that the amount of energy carried by a photon could be found by multiplying just two numbers. These were the light’s frequency and a number we now call the Planck constant. His equation said E = hf, where E is energy, h is the Planck constant, and f is frequency.

Clearly a photon could only carry an amount of energy that was a multiple of one number – Planck’s constant. All other energies were forbidden. This was the essence of quantum theory – light was allowed to have certain amounts of energy, but was forbidden from having others.

No matter how hard Bohr worked, no matter how much literature he read, and no matter how much he discussed the problem with colleagues, he could not find a way of bringing quantum theory – in other words, allowed states and forbidden states – into the electron’s behavior in the atom.

Then, in February 1913, came the breakthrough. He heard about the Balmer Series and the Balmer Formula.

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Courtesy: Guillotined Chemistry