By:Stephanie Ng 5/5/2016
Experimental exploration in chemistry has often contributed greatly to the field since observing phenomena in the natural world may lead to new discoveries. In the case of quantum mechanics, scientists completed experiments that yielded results which didn’t align with any previously established theories. When they realized that the results could not be explained with existing ideas, they tried to define new equations that fit with the real data. In this way, they managed to build upon a field that deviated from classical mechanics, creating a flurry of activity in a new area of study, quantum mechanics.
One of the earliest experiments that contributed to quantum was Planck’s examination of blackbody radiation. He realized that the data showed a discrepancy between the experimental values of radiation and ones predicted by classical theory at high frequencies but not low frequencies. He found that a relationship between energy, an undefined constant, h, and frequency helped resolve the discrepancies. In the equation he proposed, the energy was quantized, though the frequency was continuous. This showed a strong departure from classical mechanics. Previously, energy was thought of as continuous, meaning that it could take on any value. Quantization confined energy to a set of discrete values, which was thought to be unnatural at the time.
Planck’s ideas were radical for his time, but it wasn’t long before Einstein came along to corroborate his theories. Einstein’s experiment was the photoelectric effect, which involves the process of electron ejection by light. Essentially, incident light can hit a metal surface and excite electrons to an unoccupied energy level. If the energy transferred to the electrons is of a great enough magnitude, the electrons may leave the metal. Classical mechanics was unable to predict the results of the experiment involving the emitted electrons. Einstein discovered two important ideas. First, there was a threshold of energy that needed to be overcome before any electrons were emitted at all. If the incident light did not reach this minimum threshold, then no electrons were emitted. Second, there appeared to be a relationship between the energy and frequency of the light. Surprisingly, the constant that related the frequency to the energy was discovered to be the same as Planck’s previous constant!
These experiments confirmed the idea that a new system different from classical mechanics was necessary .In the end, quantum mechanics was an interesting foray into experimental practices producing new theories. Even so, it was difficult for many people to accept since the ideas for classical mechanics had been entrenched in the scientific community for a long time. But progression of scientific exploration is important, and now, quantum mechanics has cemented its place in chemistry classrooms everywhere.