Chemical Compound Naming Rules

Overview

This lecture covers how to identify and correctly name both ionic and covalent (molecular) compounds, including rules for different scenarios such as transition metals and polyatomic ions.

Identifying Compound Types

• Ionic compounds consist of one metal and one nonmetal.
• Covalent (molecular) compounds consist of two nonmetals.

Naming Ionic Compounds

• For ionic compounds without a transition metal: name the metal first, then the nonmetal ending with "ide."
• Charges must be balanced so the overall compound is neutral.
• Use subscripts to balance charges between ions (e.g., Al₂O₃ for aluminum oxide).

Ionic Compounds with Transition Metals

• Name the transition metal, add its charge as a Roman numeral in parentheses, then the nonmetal ending in "ide."
• Transition metals can have multiple possible charges; the Roman numeral specifies which one.
• Example: Fe₂O₃ is iron (III) oxide.

Polyatomic Ions in Ionic Compounds

• Polyatomic ions contain two or more elements and have specific charges to memorize.
• When naming, use the metal name plus the polyatomic ion name (e.g., calcium phosphate).
• Polyatomic ions often end in "ate" or "ite" (exceptions: hydroxide, cyanide).
• Use parentheses for subscripts in formulas containing polyatomic ions (e.g., Ca₃(PO₄)₂).

Ionic Compounds with Transition Metals and Polyatomic Ions

• Name the transition metal, its Roman numeral charge, then the polyatomic ion.
• Example: Cu(NO₃)₂ is copper (II) nitrate.

Writing Names from Chemical Formulas

• Identify each element and whether it’s a transition metal, nonmetal, or polyatomic ion.
• Assign charges based on subscripts to deduce the Roman numeral for transition metals.
• Example: FeBr₂ is iron (II) bromide; Cu₃(PO₄)₂ is copper (II) phosphate.

Naming Covalent (Molecular) Compounds

• Covalent compounds consist of two nonmetals; use prefixes to indicate the number of each atom.
• The first nonmetal keeps its name and gets a prefix if more than one atom.
• The second nonmetal gets both a prefix and ends in "ide" (e.g., diphosphorus pentoxide).
• No charge balancing is needed; the prefixes indicate quantity directly.

Key Terms & Definitions

• Ionic Compound — compound of a metal and a nonmetal with electron transfer.
• Covalent (Molecular) Compound — compound of two nonmetals sharing electrons.
• Transition Metal — metal that can have multiple ionic charges.
• Polyatomic Ion — a charged group of two or more covalently bonded atoms.
• Roman Numeral — indicates the charge of a transition metal in a compound.
• Prefix — shows the quantity of each element in a molecular compound (mono-, di-, tri-, etc.).

Action Items / Next Steps

• Memorize common ion charges and polyatomic ions.
• Study the list of prefixes for covalent compounds (1-10).
• Practice writing compound names from formulas and vice versa.