If you looked close at an atom, it would look kind of like a planetary system, right? The nucleus, made up of bundled protons and neutrons, sitting dense and stationary at the center, while a bunch of electrons, more diffuse and blurry, race in whirling orbits around the nucleus.
Right? I'm sure you were taught that in high school. Maybe even in college as well. Heck, I remember once someone teaching that to someone else on an episode of WKRP in Cincinnati. (I'm not proud of that.)
Trouble is, it's not true. That hasn't been the current model of the atom since the 1920s at the latest. In fact, it was only the predominant model for a period of a few years or decades. The preceding "plum pudding" model (in which electrons were seen as being like plums in a plum pudding, or seeds in a watermelon), originated by J. J. Thomson at the end of the 19th century, actually lasted longer. The Rutherford planetary model was almost immediately displaced by the Bohr model (which introduced shells and quanta), which was absorbed into the nascent field of quantum mechanics and became a lot more complicated.
Isn't it odd that one particular fleeting moment in the history of atomic theory, disproven almost a hundred years ago, is still being taught to essentially everyone?