In a previous lesson, you learned that Erwin Schrödinger proposed what has come to be known as the quantum mechanical model, which is the modern view of electrons in atoms. In this model, electrons are treated as waves, not particles, and these waves exist within specifically shaped clouds of probability that he called orbitals.

An atomic orbital is a three-dimensional region around the nucleus that you can picture as a fuzzy cloud. The density of the cloud at a given point relates to the probability of finding an electron at that point.

The electrons in the electron cloud are not in some random arrangement. Instead, the arrangement of electrons in atoms follows specific rules. In this lesson, you will learn and apply these rules to correctly represent the arrangement of electrons in an atom.