# In atoms, what is potential energy?

I was reading about how potential energy in atoms is measured by how far apart they are from one another. From what I have heard of potential energy, it's a way of showing how fast an object could move. E.G. if a basketball was lifted up off the ground, it could move because of more room to accelerate due to gravity. In the case of atoms, though, I don't see why the potential to move is dictated by how far apart the atoms are from one another. Could someone please explain?

• What you mean by how far apart are the atoms? I a rarefied gas the atoms are far apart until they collide. In a lattice, the distance between atoms is established by the geometry of the lattice. So, how far apart are the atoms in which situation, in which form of aggregation? Moreover, the potential energy in an atom establishes first of all the movement of the electrons of the atoms, not positions of other atoms. So, it's not clear how correct is what you heard. – Sofia Jan 31 '15 at 1:57
• Ok. I recall reading it in physics class, though I might not remember correctly. It said that if atoms were more densely packed (like ice) it would have less potential energy than if it was less densely packed. (like vapor) It sounds like the lattice model would fit what I recall. Potential energy as the speed of electrons makes a lot more sense. – Code Cube Jan 31 '15 at 3:43
• I also remember it showing a chart where, as thermal energy is added to ice, the kinetic energy increases for a while. Then, when it hits the melting point, it stops receiving kinetic energy and stores up potential energy instead. How do the electrons going faster cause a state change? – Code Cube Jan 31 '15 at 3:45

Usually this level of potential energy infinitely far away is set to be $0$. Then, the closer they come, the more negative the potential energy becomes.
In that case, we usually still define "infinitely far from each other" to be the potential energy of $0$ joules. So the closer two equal charges get, the more positive the potential energy is (meaning, larger potential to speed up the charges). And if you let them go, they will seek towards lowest possible potential energy, which is the case when they are infinitely far from each other again.