Naming & Writing Chemical Formulas

Compound Classification

• Ionic Compounds: Formed from a metal bonded with a nonmetal, or a metal bonded with a polyatomic ion.

• Covalent (Molecular) Compounds: Formed when nonmetals share electrons.

• Binary Compounds: Composed of exactly two different elements (e.g., $MgCl_2$, $CO_2$).

• Ternary Ionic Compounds: Composed of three or more elements by incorporating at least one polyatomic ion (e.g., $Ca(NO_3)_2$, $Na_2SO_4$).

Ionic Compound Formulas and Particle Models

• Main-Group Ion Charges:

  • Group 1: $+1$

  • Group 2: $+2$

  • Group 13: $+3$

  • Group 15: $-3$

  • Group 16: $-2$

  • Group 17: $-1$

• Charge Balance Principle: Cations and anions combine in the smallest whole-number ratio such that total positive charge and total negative charge equal zero (e.g., $Mg^{2+} + 2Cl^- \rightarrow MgCl_2$).

• Subscripts: Written in simplest whole-number ratios; the subscript $1$ is never explicitly written.

• Polyatomic Ions: Discrete groups of covalently bonded atoms bearing a net charge. Parentheses enclose polyatomic ions whenever a subscript greater than $1$ is required (e.g., $Al_2(SO_4)_3$).

• Particle Models: Illustrate stoichiometric ratios of ions maintaining neutral charge; ionic solids exist as repeating three-dimensional crystal lattices rather than independent molecular units.

Naming Ionic Compounds

• Binary Ionic Compounds:

  • Name the cation (metal) first using its standard element name.

  • Name the anion (nonmetal) second, altering the ending to -ide (e.g., $NaCl$ is sodium chloride; $Al_2S_3$ is aluminum sulfide).

  • Prefixes are never used in ionic compound names.

• Transition Metals with Variable Charges:

  • A Roman numeral placed in parentheses immediately after the metal indicates the ionic charge of the cation, not the quantity of atoms.

  • Examples: $FeCl_3$ contains $Fe^{3+}$ and is named iron(III) chloride; $Cu_2O$ contains $Cu^+$ and is named copper(I) oxide.

Naming Binary Covalent Compounds

• Prefix Rules: Greek numerical prefixes indicate the quantity of atoms of each element:

  • $1 = \text{mono-}$ (omitted on the first element)

  • $2 = \text{di-}$

  • $3 = \text{tri-}$

  • $4 = \text{tetra-}$

  • $5 = \text{penta-}$

  • $6 = \text{hexa-}$

• Naming Structure: The first element keeps its elemental name (with prefix if greater than one); the second element receives a prefix and the -ide suffix (e.g., $CO$ is carbon monoxide; $CO_2$ is carbon dioxide; $N_2O_4$ is dinitrogen tetroxide).

Acid Nomenclature and Common Formulas

• State Requirement: Laboratory acids are aqueous solutions denoted by the state symbol $(aq)$.

• Binary Acids: Hydrogen plus a single nonmetal in aqueous solution follow the pattern: $\text{hydro-} + \text{nonmetal root} + \text{-ic acid}$ (e.g., $HCl_{(aq)}$ is hydrochloric acid).

• Oxyacids: Hydrogen plus a polyatomic oxyanion (the prefix hydro- is omitted):

  • Polyatomic ions ending in -ate become -ic acid (e.g., nitrate $\rightarrow$ nitric acid; sulfate $\rightarrow$ sulfuric acid).

  • Polyatomic ions ending in -ite become -ous acid (e.g., nitrite $\rightarrow$ nitrous acid; sulfite $\rightarrow$ sulfurous acid).

• Common Laboratory Acids:

  • Hydrochloric acid: $HCl_{(aq)}$

  • Nitric acid: $HNO_{3(aq)}$

  • Sulfuric acid: $H_2SO_{4(aq)}$

  • Phosphoric acid: $H_3PO_{4(aq)}$

  • Acetic acid: $HC_2H_3O_{2(aq)}$ or $CH_3COOH_{(aq)}$

  • Carbonic acid: $H_2CO_{3(aq)}$