Physics
Ground State Energy
Quick fact
The ground state energy of a hydrogen atom is -13.6 eV, which means it would take that much energy to strip the electron away, but the electron itself always retains a minimum kinetic energy due to quantum fluctuations.
Why this is interesting
Imagine if you could drain all thermal energy from a particle until it's 'completely still' – in the quantum world, that's impossible. Why does every atom have a minimum energy it can never lose?