Ions and Ionic Compounds

Understand how ions are formed and the underlying principles governing their stability.
Learn the characteristic charges that ions possess based on their position in the periodic table.
Be able to construct a proper formula for an ionic compound, ensuring charge neutrality.
Learn to generate a proper name for an ionic compound following IUPAC nomenclature rules.

Elements and compounds are typically electrically neutral, possessing an equal number of electrons and protons. This balance ensures stability.
Ions are formed when electrons move from one atom to another, resulting in species with an overall electric charge. This transfer is driven by the attainment of a stable electron configuration.
- Cations: Species with an overall positive charge, formed when an atom loses one or more electrons.
- Anions: Species with an overall negative charge, formed when an atom gains one or more electrons.

Key point: Ions are formed by the movement of electrons, not protons. The number of protons defines the element, so changing it would alter the element itself.
Ionic compounds are formed from positive and negative ions through electrostatic attraction, creating a crystal lattice structure.
Individual atoms can gain or lose electrons, becoming monatomic ions. The charge of the ion depends on the balance between protons and electrons.
Atoms usually gain or lose a characteristic number of electrons, resulting in a characteristic overall charge. This tendency is related to achieving a stable electron configuration, often resembling that of a noble gas.

Metals tend to form cations, while nonmetals tend to form anions. This is a chemical property of metals and nonmetals, related to their ionization energies and electron affinities.
Most atoms form ions with a single characteristic charge, predictable from their group number in the periodic table.
- Example: Sodium atoms always form a 1+ charge (Na+), as losing one electron gives it the same electron configuration as neon.

Ions formed by losing two electrons
- Mg2+, Ca2+, Sr2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Sn2+, Hg2+, Pb2+

Ions formed by losing three electrons
- Sc3+, Fe3+, Co3+, Ni3+, Au3+, Al3+, Cr3+

Some metals can form more than one possible charge. This is due to the relatively small energy difference between removing different numbers of electrons from their outer shells.
- Example: Iron can form Fe2+ or Fe3+, depending on the reaction conditions.
- Other examples: Cobalt (Co2+ and Co3+), Lead (Pb2+ or Pb4+).

It is best to memorize the possible charges for these elements to accurately predict compound formation and nomenclature.

The magnitude of the charge is written as a right superscript next to the element symbol to denote the ion.
If the charge is a single positive or negative one, the number 1 is not written (e.g., Na+ implies a charge of +1).
If the magnitude of the charge is greater than 1, the number is written before the + or − sign (e.g., Mg2+ indicates a charge of +2).
An element symbol without a charge indicates an uncharged atom, which is electrically neutral.

Cations: Use the element name followed by "ion" or "cation."
- Example: Na+ is the sodium ion; Ca2+ is the calcium ion.

For elements with multiple possible charges, specify the charge using Roman numerals in parentheses after the element name. This is necessary to distinguish between different ions of the same element.
- Example: Fe2+ is the iron(II) cation; Fe3+ is the iron(III) cation.

Anions: Use the stem of the element name, append the suffix "-ide," and then add "ion." This convention is consistent for all monatomic anions.
- Example: Cl− is the chloride ion; N3− is the nitride ion.