Quantum Mechanics
Quantum Mechanics is Weird!
When we think of an atom, a common approach is to see an electron orbiting around the nuclei, perhaps as shells that move around a circular orbit as if they were planets around a star. But this is way different in this complicated world where quantum mechanics dominate in the microscopic scale!
In reality, molecules can only exist in certain quantised (discrete states).
Quantum mechanics was largely developed from the 1920’s onwards by Schrodinger, Dirac, etc
Energy levels within molecules are quantised, discrete, just like steps.
Atomic Orbitals
Electrons are found in orbitals surrounding the nucleus around the atom. Atomic orbitals are a region of space where up to 2 electrons can be held with opposite spins.
The uncertainty principle
The uncertainty principle states that the more we know about one's mass and velocity, the less likely we are to know its exact position or vice versa. It is better seen for orbitals if they were rather a sort of probability space of which an electron is most likely to reside, than if orbitals were seen as a set trajectory for which the electrons 'hover' around.
Probability densities and the famous Schrodinger's cat
When Quantum Mechanics looks at the wave nature of matter, it's mostly concerned with the probability that particles, like electrons or even atoms, will be in certain places at certain times. That probability is predicted by the Wave Function ( Ψ ), the equation used to find this was derived by Erwin Schrödinger in the 1920's and relates some of the properties of a quantum mechanical system. One of the main reasons that the equation is useful is that it helps us to predict the probability of finding a particle at any given point in space known as the Probability Density Function. The orbitals mentioned further up the page are a graphical representation of the probability density function and their shape is calculated using Schrödinger's Equation.
Let's set up a thought experiment to investigate this idea of probability density. If you had a box with a particle inside, an electron for example, which can be at any point within the box and each point has a probability of the particle being there. Once you open the box you can see the particle is at a position within the box. Many physicists believe that while the box is closed the particle can be said to be at various positions within the box even at the same time. This idea of one particle being in more than one state at the same time is an example of Quantum Superposition, an idea that Schrödinger himself explored in his famous thought experiment 'Schrödinger's Cat'. Schrödinger's experiment goes as such; A cat is left in a box with a sealed vile of poisonous gas which will only break open when a radioactive atom decays. If the box is not open and we don't know whether the poison has been released the cat can be thought of as both dead and alive at the same time much like the particle in our experiment can be thought of as being in multiple positions at once.
