How can you tell the difference in a Lewis Acid and a Lewis Base?

Question

aaronq · Answer

lewis acid accepts electrons, lewis base donates electrons

anonymous · Answer

That makes sense. But what if you have a list of elements and have to choose from them? For example, I have $$NH _{3}, H _{2}O, CH _{4}, and  CN-$$

aaronq · Answer

i find the bronzed-lowry definition better, and they're the same thing, but they talk about protons. 

SO an acid is a proton donor, and a base a proton acceptor

so NH3 can accept a proton and become NH4+ so it's a base
or it can donate a proton and become NH2-

All substances can act as acids and bases, but the way they act in depends on their surroundings (molecules they're reacting with)

aaronq · Answer

bronsted*  i dislike autocorrect

anonymous · Answer

The answer key I have says that CH4 is the only one of the ones I listed above that is not a potential base. Do you know why?

aaronq · Answer

because it can't accept a proton since it can't make more than 4 bonds

(sorry my internet cuts out often)

anonymous · Answer

Oh that makes sense! Thanks!

aaronq · Answer

no prob!