Electric charge is a basic property of elementary particles of matter. The protons in an atom have a positive charge, while its electrons have a negative charge. In an ordinary atom, the number of protons equals the number of electrons, so the atom is electrically neutral. If an atom gains some electrons, it becomes negatively charged. If it loses some electrons, it becomes positively charged. Atoms that become charged are called ions. Every charged particle is surrounded by an electric field, the region of space in which the charge exerts a force. Because of their electric fields, particles with unlike charges attract one another, and those with like charges repel one another. Static electricity consists of charged particles at rest. Electric current consists of moving charged particles, especially electrons or ions.