Section 1: Chemical Names and Formulas
Significance of a Chemical Formula
Indicates relative number of atoms in a compound.
Molecular compounds: shows number of atoms in a molecule (e.g., $C<em>{8}H</em>{18}$).
Ionic compounds represent one formula unit (e.g., $Al<em>{2}(SO</em>{4})<em>{3}$). Monatomic Ions Formed from a single atom. Cations: element's name (e.g., $K^{+}$ is potassium cation). Anions: root name + -ide (e.g., $F^{-}$ is fluoride anion). Common Monatomic Ions Cations: Li$^{+}$ (Lithium) Na$^{+}$ (Sodium) Mg$^{2+}$ (Magnesium) Anions: F$^{-}$ (Fluoride) O$^{2-}$ (Oxide) N$^{3-}$ (Nitride) Naming Binary Ionic Compounds Combine names of positive and negative ions (e.g., $Al</em>{2}O<em>{3}$ is aluminum oxide). Use "crossing over" method to write formulas: Write cation and anion symbols. Cross the charges as subscripts. Stock System of Nomenclature Used for elements with multiple charges (e.g., Iron(II) $Fe^{2+}$, Iron(III) $Fe^{3+}$). Compounds Containing Polyatomic Ions Oxyanions: ions containing oxygen. Named with -ate or -ite suffix based on the number of oxygen atoms: -ate: More oxygen atoms (e.g., $NO</em>{3}^{-}$ is nitrate).
-ite: Fewer oxygen atoms (e.g., $NO<em>{2}^{-}$ is nitrite). Example: Chlorine Oxyanions Chlorate: $ClO</em>{3}^{-}$
Chlorite: $ClO<em>{2}^{-}$ Hypochlorite: $ClO^{-}$ Perchlorate: $ClO</em>{4}^{-}$
Naming Molecular Compounds
Use prefixes to denote the number of atoms of each element in the compound. For example, in $CCl<em>{4}$: Carbon (1) - no prefix Chlorine (4) - tetra- prefix Prefixes: mono- (1), di- (2), tri- (3), tetra- (4), penta- (5), hex- (6), hepta- (7), octa- (8), nona- (9), deca- (10). The first element in the compound keeps its full name, while the second element’s name is modified to end in -ide (e.g., $N</em>{2}O$ is dinitrogen monoxide).
Acids and Salts
Binary acids: two elements, e.g., $HCl$ (hydrochloric acid).
Oxyacids: contain hydrogen, oxygen, and another element (e.g., $H<em>{2}SO</em>{4}$ - sulfuric acid).
Salts: formed from ionic compounds with ions derived from acids (e.g., $NaCl$ from $HCl$).