Overview
Descriptive chemistry focuses on the properties, behaviors, and trends of elements and compounds. This includes recognizing common groups on the periodic table, identifying physical and chemical characteristics, and applying naming rules (nomenclature) to ionic and molecular substances.
Key Concepts and Structures
- Periodic Table Groups:
- Alkali Metals (Group 1): Very reactive, especially with water
- Alkaline Earth Metals (Group 2): Reactive, form +2 ions
- Halogens (Group 17): Very reactive nonmetals, form -1 ions
- Noble Gases (Group 18): Inert, stable gases
- Transition Metals: Variable oxidation states, often form colored compounds
- Physical Properties: Melting point, boiling point, color, state (solid/liquid/gas), density, conductivity
- Chemical Properties: Reactivity, acidity/basicity, combustion, oxidation state trends
- Metal vs. Nonmetal Behavior: Metals lose electrons to form cations; nonmetals gain electrons to form anions
- Binary Ionic Compounds: Name metal first, then nonmetal with "-ide" suffix.
Example: NaCl → sodium chloride
- Transition Metal Compounds: Use Roman numerals to indicate charge.
Example: FeCl₂ → iron(II) chloride
- Molecular Compounds: Use prefixes (mono-, di-, tri-) for both elements.
Example: CO₂ → carbon dioxide
- Acid Nomenclature:
- Binary acids: "hydro-" + base name + "-ic acid" (e.g., HCl → hydrochloric acid)
- Oxyacids: Based on polyatomic ions (e.g., H₂SO₄ → sulfuric acid)
- Common Polyatomic Ions:
NO₃⁻ = nitrateSO₄²⁻ = sulfateCO₃²⁻ = carbonateNH₄⁺ = ammoniumOH⁻ = hydroxide
Quick Tip
Memorize the most common polyatomic ions and the naming rules for acids and ionic compounds—they show up frequently on the CLEP exam and are easy points if you know the patterns.