Ions
Normally, atoms are neutral. They have the same number of Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1. in the The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei. as they have Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. orbiting in the Specific amounts of energy that electrons have when they orbit a nucleus is a particular shell. Electrons that gain energy may move to a higher energy level (a shell further from the nucleus). Electrons that lose energy may move to a lower energy level (a shell closer to the nucleus). around the nucleus.
Atoms can, however, lose or gain electrons due to collisions or other interactions. When they do, they form charged particles called Electrically charged particle, formed when an atom or molecule gains or loses electrons.:
- if the atom loses one or more electrons, it becomes a positively-charged ion
- if the atom gains one or more electrons, it becomes a negatively-charged ion
A helium atom has two electrons in an energy level outside the nucleus. The atom is neutral as it has two positive protons and two negative electrons.
A helium atom that has lost or gained an electron is an ion.
Image caption, The ion has two positive protons but one electron so it is a positive ion
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