Questions about extremely sharp blade.

What kind of movement are you using on the metal or concrete? A strike or a swipe?

Is this in the real world or in a fantasy world?

Even with a very sharp blade it has to go through something solid. Cutting through a piece of cloth by dropping it on the blade doesn't happen in the real world.

Even if you are dreaming about single molecule thick bldes, then there still is the matter of pulling it through things.

Your blade is composed of atoms. For it to cut through chemical bonds would require it to be made of something smaller than the bonds themselves, so probably not atoms. Seems to be taking an idea to an absurd and unnecessary length. What significance does this have to your story? What difference is there between a very sharp blade, and a blade that can 'cut chemical bonds' to your story? Is there a point in the story where the protagonist has to produce chlorine gas from salt or something that such a weapon would be necessary? The only special power of such a weapon would be to piss off those of us who are scientifically inclined.

Besides, atomic bonds are not 'cut' physically, the idea may even be nonsensical. Even the idea of a chemical bond is a simplification. Its more of a state of balance in forces than a physical thing. You can't take concepts that work on one scale and assume they work on very different scales: Things are fundamentally different on the atomic scale, and your 'common sense' doesn't function there.

Are we talking real swords or other edged weapons here?

Why would you WANT to cut metal or stone in the first place? No matter how sharp the edge is, you'll more than likely inflict damage to the blade itself. A sword is designed to cut through flesh and bone.

Many blades, depending on the quality of the steel, allow a near razor sharp edge. But like kitchen knives, with constant use they still need to be maintained and sharpered. But abuse like you're talking about... Why?

And what do you mean by "chemical bonds"?

If you're curculio us about what a sword can do, there are plenty of YouTube videos out there. Just search for "sword test" or "sword review." There's also a website called Sword Buyers Guide that has reviews of modern swords. Sometimes they test to failure by striking at metal objects, like 50 gallon drums and the like.

Well, in that case... It's your fantasy world, your story... Those physics are up to you. Do you WANT it to take some effort or no effort at all? Really depends on what you need for your story.

If you just want to see how much force it takes, youtube has videos of swords cutting about anything you can imagine. Here's one to get you started.
http://www.youtube.com/watch?v=u3nAuowwqhI

It sounds like you're talking about a laser-sharpened edge, which in popular fiction are "molecules thick" at the edge, meaning that they'd slice into skin before you knew you were close enough to be wounded.

Yes, a thinner edge can be sharper, but it's also weaker, and even something a molecule thick is still thicker than the bond between the atoms creating the molecule. Go thinner and you're into composite elements, which means you've compromised the integrity of whatever compound makes up your sword.

Now if this is a fantasy world with some kind of magic system, then sure - make it thin as a thought and sharp as wit, no one will think twice. But also consider why concrete would exist in a fantasy world. It's not a naturally occurring substance.

i guess, as mentioned, I'm not sure what purpose this would serve. as mentioned, when would you "cut molecules"? Even if the guy was in a room with chlorine gas or something similar, are we now also supposed to believe he can see individual molecules, and cut them by the thousand in a fraction of a second? It is your world, as mentioned, but the more implausible you make it the harder the sell. In this case, other than your sense it would be "cool," I'm not sure there's a payoff....but it isn't my story and you would know more than I do.