HOW TF DO I MEMORISE EVERY SINGLE THING IN CHEM???

Chem me mai saare chapters revise kar raha hu 5 times, but jab paper deta hu to koi aisa small topic se question aa jata hai jo maine dekha bhi nahi tha revision ke time. Maths thik thak hota hai 50s me aajate hain but physics me questions me dimag nhi laga paata and 60s me aate hain aur chem ka bhi chhote chhote cheeze reh jaati hain. Pls help