An ion is an atom with unequal number of electrons and protons. In other words, an ion is an electrically charged atom, which has a negative or positive electric charge. If the electron count is higher than neutrons, the atom has a negative charge, and is called an anion or negative ion. Similarly, if protons are higher in population, the atom’s positively charged, and is called cation or positive ion. Ions tend to stand out because atoms are usually neutrally charged, or have equal number of protons and electrons.
A positive or negative atom is indicated with a superscript placed next to its chemical symbol. For example, carbon is a positive atom as it has five electrons and six protons. Therefore, it’s symbolized as C+. If an atom’s electron and proton difference is more than 1, the surplus is indicated with a number accompanying the superscript symbol. For example (hypothetically), if the protons outnumber the carbon atom’s electron count by three, the difference would be denoted as C3+.
Generally, the proton count of an atom doesn’t change. Electrons are usually shifting places or atoms. An ion is formed when an atom gains or loses electrons. For example, hydrogen has only one proton and electron. When it gains an electron, it ends up with two electrons. This means it becomes negatively charged and becomes an anion called hydride.
Electrons can move between atoms and an electron loss or gain can alter an atom’s electric charge. However, its core identity doesn’t change with electron movement. An atom’s identity is based on its proton population. For instance, an oxygen atom has eight protons in its nucleus. If there were one proton less, the oxygen atom will become nitrogen, which has seven protons.