Many but not all of these topics are essential to know and/or understand before starting a degree in chemistry at a university.
I've organised the following list of topics so that the most fundamental concepts come first, but learning the concepts in this order is certainly not the best way, nor the easiest way, to learn chemistry.
The list is for checking what you've missed during (or have forgotten since) your study of chemistry at school.
I'm also compiling a list of chemistry things to un-learn after A-level, to make it easier to get into the swing of things at university. The fact that it is possible for me to write such a list suggests that the people who decide what we learn at school, and how we learn it, could do better!