i just need an explanation :) so the problem was " what is the mass of 5 molecules of water(H2O) , in grams?" my teacher said the answer is 1.50 x 10^-22 but i dont understand why. why is it not 1.50 x 10^24, why is the exponent negative?

Explanation:

The exponent is negative because water molecules are absolutely tiny. You can't see a molecule of water on the palm of your hand with your naked eyes, right? If a the mass of a molecule was 1.50 x 10^24, it'd be HUGE... like absolutely massive (possible the size of your city). Molecules are just tiny, tiny particles

they are made of gases.

they have a spherical shape.

they make energy through fusion.