An atom is composed of three fundamental subatomic particles that determine its characteristics and charge. These particles include the proton, which carries a single positive electrical charge, and the electron, which carries an equal and opposite single negative electrical charge. The third particle, the neutron, is also found within the atom’s center but has no electrical charge.
Atomic Structure: Protons, Electrons, and Charge
A neutral atom serves as the baseline for understanding electrical charge in matter. In this balanced state, the number of positively charged protons exactly matches the number of negatively charged electrons.
The number of protons within an atom’s nucleus is unique to that element and is called the atomic number. This number is the defining characteristic of an element; for instance, every atom with 11 protons is a sodium atom. Crucially, the number of protons in an atom’s nucleus remains unchanged during common chemical reactions. Therefore, any shift in the atom’s overall charge must involve a change in the number of electrons orbiting the nucleus.
Defining a Positive Ion (Cation)
A positive ion contains more protons than electrons. This charged particle, formally known as a cation, is created when the atom develops a net positive charge. The positive charge is not due to an increase in the number of protons, but rather a deficit of negatively charged electrons.
For every electron lost by the atom, the overall positive charge increases by one unit. For example, if a neutral sodium atom with 11 protons and 11 electrons loses one electron, the resulting cation still has 11 protons but only 10 electrons, giving it a net charge of +1 (Na\(^{+}\)).
The Process of Ion Formation
Atoms will lose or gain electrons to achieve a more stable electronic configuration. For many elements, this stability is reached when the outermost electron shell, or valence shell, is full, which often means having eight valence electrons.
Elements that form positive ions, such as metals, typically have only one or two electrons in their outer shell and tend to lose them to satisfy this stability rule. This electron loss is often driven by a chemical reaction, such as when an atom transfers its valence electrons to another atom.
Conversely, a negative ion (anion) forms when an atom gains electrons, leading to an excess of negative charge. The formation of cations allows atoms to bond together, forming ionic compounds like table salt (sodium chloride).