All I know is that one is covalent while the other is ionic, and that having hydrogen in the mix will automatically make it covalent since it will distinguish if it’s polar on non-polar. Also, I read something about certain elements and/or compounds being naturally covalent/ionic, the thing is, how do you know? Feel free to correct anything I’ve said wrong, and please, help me Thanks!

I need an explanation for a complete novice here, so the for dummies version would be very much appreciated:
In calculating the mean free path of something, there’s this formula: 2.5 x 10 (-3, which is raised). What does each individual component mean? And if the numbers were 2.7 x 10 (-6), would the end result be bigger? Also, is the second number always ten?
Help with an explanation, and links to any physics and chemistry sites that are written in plain language would be fantastic. Thank you.