Chargeneutral

Chargeneutral, or charge neutrality, describes the condition in which the total electric charge of a system is zero. In other words, the number of positive charges (protons) balances the number of negative charges (electrons), so the net charge Q equals zero. Individual constituents may be charged, but their charges sum to zero for the whole system.

In atoms and molecules, a neutral atom has equal numbers of protons and electrons. Ionic compounds contain oppositely charged ions in proportions that cancel overall. In bulk materials, charge neutrality is a guiding principle: despite possible local variations in charge, the macroscopic material behaves as electrically neutral.

In plasmas, the concept is refined to quasi-neutrality. On length scales larger than the Debye length, electron and ion densities are nearly equal, so there is no large-scale electric field. Near boundaries or within sheaths, charge separation can occur and local electric fields arise.

In technological contexts, maintaining charge neutrality is important for devices and processes. Semiconductor devices rely on balancing charge carriers; electrode materials in batteries exchange charge yet are overall electrically neutral. Doping or charging can create local imbalances that drive currents or alter electrical properties.

In cosmology and fundamental physics, the universe is observed to be electrically neutral on large scales. Any tiny net charge would produce strong fields that would tend to redistribute charges rapidly, so charge neutrality is considered a fundamental global property of matter as currently understood.