Final answer:
The electrostatic energy of a crystal containing positive and negative charges can be represented by the potential energy series. This energy is always required to separate the ions, making it positive. The distance between the ions and their charges determines the potential energy.
Step-by-step explanation:
The electrostatic energy of a one-dimensional crystal containing alternating positive and negative charges can be represented by the potential energy series.
In this series, the energy is always required to separate the ions, making the lattice energy positive. This energy can be estimated using a Hess Law approach or calculated from the electrostatic consideration of the crystal structure.
For example, in the NaCl crystal, the electrostatic potential of a single ion can be approximated by the point charges of the surrounding ions. The potential energy is determined by the distance between these ions and their charges.