5.8 Common and Systematic Names In the early days of chemistry, a new compound was often named by its discoverer. In the early days of chemistry, a new compound was often named by its discoverer. These common names often described a physical or chemical property of the substance or the source of the compound. These common names often described a physical or chemical property of the substance or the source of the compound. Examples: Examples: Potash is the common name for KCO 3 (potassium carbonate) – the compound was separated by boiling wood ashes in iron pots. was separated by boiling wood ashes in iron pots. Laughing gas is the common name for N 2 O (dinitrogen monoxide) – this gas makes people laugh when inhaled

5.8 Common and Systematic Names Commons names are often very descriptive, however they do not tell you anything about the chemical composition of the compound. Commons names are often very descriptive, however they do not tell you anything about the chemical composition of the compound. As the science of chemistry developed, it was apparent that a systematic method for naming chemical compounds was needed (a standard set of rules to follow when naming compounds). As the science of chemistry developed, it was apparent that a systematic method for naming chemical compounds was needed (a standard set of rules to follow when naming compounds).

5.9 Writing Formulas for Binary Ionic Compounds Binary compounds are composed of two elements. Binary compounds are composed of two elements. Example: Potassium chloride is a binary compound formed from potassium cations (K + ) and chloride anions (Cl - ). Example: Potassium chloride is a binary compound formed from potassium cations (K + ) and chloride anions (Cl - ). Ionic compounds have to be electrically neutral so the ions that form them must combine in a ratio that balances their charges. Ionic compounds have to be electrically neutral so the ions that form them must combine in a ratio that balances their charges. Since [K + ] has a +1 charge and [Cl - ] has a -1 charge they combine in a 1 to 1 (1:1) ratio to form KCl. Since [K + ] has a +1 charge and [Cl - ] has a -1 charge they combine in a 1 to 1 (1:1) ratio to form KCl.

5.9 Writing Formulas for Binary Ionic Compounds Rules for writing formulas: 1. Write the symbol for the cation. 2. Write symbol for anion. 3. Identify ionic charges on the ions. 4. Add subscripts to balance charges. * Never use 1’s as subscripts ** The crisscross method can be used to determine the subscripts.

5.9 Writing Formulas for Binary Ionic Compounds What would be the ratio of ions and formulas for the following ionic compounds? What would be the ratio of ions and formulas for the following ionic compounds? Calcium bromide Calcium bromide Ions: [Ca 2+ ] [Br - ] Ions: [Ca 2+ ] [Br - ] Ratio: 1 to 2 (1:2) Ratio: 1 to 2 (1:2) Formula: CaBr 2 Formula: CaBr 2 Iron (III) oxide – “crisscross” method Iron (III) oxide – “crisscross” method Ions: [Fe 3+ ] [O 2- ] Ions: [Fe 3+ ] [O 2- ] Ratio: 2:3 Ratio: 2:3 Formula: Fe 2 O 3 Formula: Fe 2 O 3

5.10 Naming Binary Ionic Compounds Rules: 1. Write the name of the cation. A. If the cation has more than one possible ionic charge a roman numeral must be used in the name to indicate the charge. B. Determine which ion it is by balancing the charges. 2. Write the name of the anion (-ide ending)

5.10 Naming Binary Ionic Compounds Example: NaCl Example: NaCl 1. Na + : sodium cation 2. Cl - : chloride anion Name: sodium chloride Example: CuO Example: CuO 1. Cu ? (needs a roman numeral) - Since O has a 2 - charge and the compound is in a 1:1 ratio it is the copper (II) cation 2. O 2- : oxide anion Name: copper (II) oxide

5.10 Naming Binary Ionic Compounds What would be the names for the following ionic compounds? What would be the names for the following ionic compounds? MgO MgO 1. Mg 2+ : magnesium cation 2. O 2- : oxide anion Name: magnesium oxide SnO 2 SnO 2 1. Sn 4+ : tin (IV) cation 2. O 2- : oxide anion Name: tin (IV) oxide