Software for drawing diagrams etc.

Hi there! Started studying this summer and going through some basic physics, chemistry and math before i jump into an engineering program. I have come to the conclusion that i learn better by taking notes on the computer. My only problem is for chemistry and physics to have well drawn diagrams and models etc. That i can just printscreen and atatch to my notes in Word. So my question is if anyone has any recomendations for a good desktop app or website (pref for free or a low monthly cost) that can help me draw physics and chemistry diagrams aswell as having all the special signs that word have to freely write with.

Pictures for reference*