Natural Sciences


Definition of ion

An ion is an atom or a group of atoms that has a total positive or negative charge. The name ion comes from the Greek word ion which means “that goes”, because the charged particles go towards or away from a charged electrode.

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Ionization is the formation of electrically charged molecules or atoms. Atoms are electrically neutral since negatively charged electrons are equal in number to positively charged protons in nuclei. The number of protons in an atom remains the same during common chemical changes (called chemical reactions), but electrons can be lost or gained.

The word ion comes from the Greek ἰών [ion], which means ‘that goes’. This word was used for the first time in the English language in 1834 thanks to the scientist Michael Faraday, who in 1830 had proposed the existence of ions. Then, in 1884, the scientist Arrhenius developed the theory that led to its verification.

Ions are formed by ionization. The term refers to the phenomenon of gain or loss of electrons from the atom when it is subjected to certain processes. The loss or gain of electrons allows the atom to acquire an electric charge, transforming itself into an ion. If the electric charge is positive, it is called a cation; if it is negative, it is called an anion. It is concluded that the non-ionized atoms are electrically neutral.

Types of ions

    • Anion : they are negatively charged ions. They are created as a result of the gain of electrons, that is why their main characteristic is the possession of more electrons than protons.

Examples of anions:

  1. Arsenide As 3−
  2. Azide N 3−
  3. Bromide Br 
  4. Carbide C 4−
  5. Fluoride F 
  6. Phosphide P 3−
  7. Oxide O 2−
  8. Peroxide O 2−
  9. Sulfide S 2−
  • Cation: they are ions that are known to have a positive charge and arise as a result of the loss of electrons. That is why they have more protons than electrons.

Examples of cations:

  1. Calcium Ca 2+
  2. Chromium (II) Cr 2+
  3. Copper (I) Cu +
  4. Iron (II) Fe 2+
  5. Mercury (II) Hg 2+
  6. Nickel (III) Ni 3+
  7. Silver Ag +
  8. Lead (IV) Pb 4+
  9. Potassium K +
  10. Sodium Na +
  11. Zinc Zn 2+

An atom can lose or gain more than one electron, such as the ferric ion with three positive charges (Fe + 3) and the sulfide ion with two negative charges (S =). These ions, like the sodium and chloride ions, are called monatomic ions because they contain only one atom. With some exceptions, metals tend to form cations and non-metals, anions.

Furthermore, it is possible to combine two or more atoms and form an ion that has a net positive or negative charge. Ions that contain more than one atom, such as OH- (hydroxide ion), CN- (cyanide ion), and NH4 + (ammonium ion) are called polyatomic ions.

The minimum energy required to separate an electron from an isolated atom (or ion) in its ground state is known as ionization energy , and it is represented in kJ / mol. The magnitude of this energy is a measure of how “tightly” the electron is bound to the atom. The higher the ionization energy, the more difficult it is to remove the electron from the atom.

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