Charge density is the amount of charge per unit volume but what is charge? I was studying about x ray crystallography and my book says that charge density is measured in electrons per nano-meter cubed and this means that charge is the amount of electrons. But i am not sure if this definition (charge density = the number of electrons in a unit volume) applies when we are studying crystallography only. So to make sure, is charge simply the amount of electrons ?
An electron has a charge (lets say $e [C]$). If you have a certain amount of electrons in a certain volume ($V [m^3]$), you have a certain charge per volume $\rho = e/V [\frac{C}{m^3}]$. Which is a density.