Hi, I'm Robin Higgins and this is an explanation of why the radius of an atom cannot be measured. Alright, so, this is definitely important question to understand conceptually. So, just to review, let's draw a typical nucleus of an atom. So, let's just say it has a bunch of protons and neutrons stuck in there and then we have going around in our traditional model a bunch of electrons and we have different orbitals, so it's different levels of electrons. So, with this model it maybe kind of confusing of why we can't simply just measure the radius and then report on that. And so, it's important to know what we're actually talking about. Just remember that an electron acts as both a particle, so we draw it as, and also a wave. And so, it's important to know that you can never actually measure exactly where an electron is at any given time. And so, what we have, when we actually draw atoms is more like our nucleus and then you'll see people draw it as an electron cloud. And so that's more like this. So, you can see that the electrons are moving so fast that we really can't draw it, even this of course is not what it looks like, it's just a complete haze. And so, first of all it would be hard to measure a cloud. And so, while we maybe able to kind of look at the cloud and know generally how big it is, and we do know how big generally atoms are, there's no way to know specifically because when would you even decided that it ended, you know, does it end here, does it end here, does it end here, and so it's something we couldn't even see little bit passed in that. And then the second thing to remember is that even it's an electron cloud, it's just based on statistics, which means that if you look into just a little tiny cross section of a specific, of a specific part of an atom electron cloud, you'll find maybe that the atom at that moment the electron cloud has a 0.00001 percent chance of being in this exact location. And then you add up all of the different percentages around here and then you have actually model all your data to make an electron cloud. So, basically the reason you can't measure the radius of an atom is because the radius is mostly determine by the electron and electron is very mysterious. Remember, they all involves in quantum mechanics, which is very difficult math, extremely difficult. I'm Robin Higgins and this is, "Why can't the radius of an atom be directly measured?"