Ions and Their Types

Monatomic Ions

Monatomic ions are ions formed from single atoms that have gained or lost electrons, resulting in a net charge. These ions are fundamental in understanding chemical bonding and reactions.

• Definition: A monatomic ion is an ion consisting of only one atom with a positive or negative charge.

• Examples:

  • Na+ (sodium ion)

  • Cl- (chloride ion)

  • Mg2+ (magnesium ion)

  • O2- (oxide ion)

• Formation: Monatomic ions are formed when atoms lose or gain electrons to achieve a stable electron configuration.

Transition Metals: Many transition metals can form more than one type of monatomic ion, often with different charges (e.g., Fe2+ and Fe3+).

Polyatomic Ions

Polyatomic ions are charged species composed of two or more atoms covalently bonded together, acting as a single unit with a net charge.

• Definition: A polyatomic ion is a group of atoms bonded together that carries a net electrical charge.

• Examples:

  • NO3- (nitrate ion)

  • SO42- (sulfate ion)

  • NH4+ (ammonium ion)

  • CO32- (carbonate ion)

• Formation: Polyatomic ions are formed when a group of atoms are covalently bonded and the group as a whole gains or loses electrons.

Common Monatomic and Polyatomic Ions

Additional info: Table entries inferred from standard chemistry knowledge and common ions.

Chemical Formulas

Basic Structure of a Chemical Formula

A chemical formula is a symbolic representation of a compound that shows the elements present and the number of atoms of each element in one unit of the substance.

• Definition: A chemical formula indicates the types and numbers of atoms in a chemical compound.

• Format: The number of atoms of each element is shown as a subscript after the element symbol.

• Order: Elements are typically listed in order of decreasing metallic character (metals first, then nonmetals).

• Example: Water: H2O (2 hydrogen atoms, 1 oxygen atom)

Types of Compounds: Ionic vs. Molecular

Ionic Compounds

Ionic compounds are formed from the electrostatic attraction between cations (positively charged ions) and anions (negatively charged ions). They typically consist of metals and nonmetals.

• Composition: Cations and anions held together by electrostatic forces.

• Structure: Arranged in a repeating three-dimensional lattice.

• Smallest unit: Formula unit (the simplest ratio of ions that represents the compound).

• Example: Sodium chloride: NaCl

Molecular Compounds

Molecular compounds are composed of nonmetal atoms bonded together by covalent bonds, sharing electrons between atoms.

• Composition: Groups of atoms (usually nonmetals) held together by covalent bonds.

• Smallest unit: Molecule (a discrete group of atoms bonded together).

• Example: Carbon dioxide: CO2

Comparison of Ionic and Molecular Compounds

Key Equations and Notation

• General formula for ionic compounds: (where charges balance)

• General formula for molecular compounds: (where x and y are subscripts indicating the number of atoms)