All matter is composed of atoms. Each atom contains a nucleus at its center, housing positively charged particles called protons and neutral particles called neutrons. Surrounding this core are negatively charged particles known as electrons, which orbit the nucleus. In a neutral atom, the number of protons equals the number of electrons, ensuring the total positive charge is canceled out by the total negative charge. This electrical balance can be disrupted, leading to the formation of particles that carry a net electrical charge.
The General Name for Charged Particles (Ions)
When an atom or a molecule gains or loses one or more electrons, it develops an overall electrical charge and is no longer neutral. Any such atom or group of atoms that bears a net positive or negative electrical charge is referred to as an ion. Ions are formed because the number of electrons no longer matches the number of protons within the nucleus. For example, a single sodium atom that loses an electron becomes a sodium ion, and a chlorine atom that gains an electron becomes a chloride ion.
Cations and Anions
The specific names for positively and negatively charged particles are cations and anions, respectively. Cations are ions that carry a net positive charge because they have fewer electrons than protons. A common example is the sodium ion (Na+), which is formed when a neutral sodium atom loses a single electron. Other examples include the potassium ion (K+) and the calcium ion (Ca2+).
Conversely, anions are ions that carry a net negative charge, meaning they have more electrons than protons. The chloride ion (Cl-) is a frequently encountered anion, created when a neutral chlorine atom gains one electron. The charge value, such as the superscript 2+ in Mg2+ or 2- in O2-, indicates the number of electrons lost or gained.
How Particles Gain or Lose Charge
The mechanism for generating a net charge relies solely on the movement of electrons, not protons. The number of protons in an atom’s nucleus is fixed and determines the element’s identity; changing the number of protons would change the element itself. Electrons occupy the outer regions of the atom, making them the particles that are transferred during chemical interactions.
When an atom loses one or more negatively charged electrons, the remaining positive charge from the protons becomes dominant, resulting in a net positive charge and the formation of a cation. Metal atoms tend to lose electrons easily to achieve stability. Conversely, when an atom gains one or more electrons, it acquires an excess of negative charge, leading to the formation of an anion. Nonmetal atoms often gain electrons to fill their outermost energy shells.