“… the existence of uncertainty need not be a source of humiliation for science… If a tiny, but crucial, uncertainty is part of the fabric of the universe, it is a tribute to scientists to have discovered the fact.” –Isaac Asimov
The Uncertainty Principle
In 1927, Werner Heisenberg proposed from a purely theoretical view that it was impossible to know both the position and momentum of the electron simultaneously. This idea, which became known as the uncertainty principle, dealt with the probability of an electron’s position in a region of space rather than its exact position.
The uncertainty principle was hard for many scientists to accept. If they accepted this idea of uncertainty, it meant that man was not capable of all knowledge and science might not be able to explain everything. But, not even Einstein could find a suitable reason not to accept the new idea.
In view of the uncertainty principle, Max Born, in 1928, suggested that the solutions to the Schrödinger wave equation be taken as a description of the probability of finding electrons in certain areas of space. These solutions in the form of numbers are called quantum numbers.
Quantum numbers not only describe specific quantized energy states for the electron but also a set of probabilities for the position of the electron in a given energy level. These probable positions known as atomic orbitals refer to a region in space where an electron might be found, whereas an orbit is a definite path in space. Since the orbital does not have definite boundaries, it is sometimes referred to as an electron cloud.
Three of the quantum numbers came directly from the Schrödinger equation. A fourth quantum number was added later by Paul Dirac to account for the affects of relativity. Together, these four quantum numbers can be used to describe the probable location of each electron. More importantly, quantum numbers can describe the electron configurations (electron arrangements) in all atoms.