As a general rule, when it comes to any science, the version you learn in grade school is extremely simplified to the point of being almost entirely useless. To draw a parallel to physics, if you ask a physicist "how many states of matter are there?", they'd probably consider it a difficult and poorly defined question, the exact distinction between a distinct state and a subset/variant of a state is up for discussion, but any coherent model has at least 20 states. What you're saying is the equivalent of "what's so hard about solid, liquid and gas?"