Models of the Atom in the 20th and 21st Centuries

The model of the atom has been contemplated since ancient Greece up to, roughly, the first half of the 20th century and one might even say that we know everything there is to know about atoms. Many facts are learned already in high school, but the average Physics or Chemistry student thinks little of how the electrons move inside the atom, or from where atoms get their mass. Indeed, how do atoms exist at all? What are the conditions of their stability? Here, we give a survey of what we know about the atom today, of the history of the models of the atom in the past hundred years or so, as well as some still unanswered questions about the atom.