Overview
This lecture covers the classification, naming, and formula mass calculations of chemical compounds, focusing on the rules for ionic, molecular, and acid compounds.
Classifying Compounds
- Compounds are classified as ionic (metal + non-metal) or molecular (non-metals only).
- Classification is needed to determine naming and formula rules.
Common Names
- H₂O is called water, not dihydrogen monoxide.
- NH₃ is called ammonia, while NH₄⁺ is ammonium (a polyatomic ion).
Ionic Compounds Naming
Type 1: Metals with Invariant Charges
- Type 1 metals form only one type of ion (e.g., Na⁺, Ca²⁺, Al³⁺).
- Naming: [Metal name] + [Non-metal base]+ide (e.g., Calcium bromide for CaBr₂).
- Do not use prefixes or indicate quantities in the name.
Type 2: Metals with Variable Charges (Transition Metals)
- Type 2 metals can form multiple ions (e.g., Fe²⁺, Fe³⁺, Cu⁺, Cu²⁺).
- Naming: [Metal name] ([Roman numeral charge]) + [Non-metal base]+ide (e.g., Iron(III) chloride for FeCl₃).
- Roman numerals specify the ion’s charge.
Polyatomic Ions in Ionic Compounds
- Use the polyatomic ion name without changing its ending (e.g., Copper(I) nitrate for CuNO₃).
- Example: Ammonium chloride for NH₄Cl.
Molecular Compounds (Covalent)
- Use prefixes to indicate the number of each atom (e.g., CO₂ = carbon dioxide, N₂O = dinitrogen monoxide).
- Do not use "mono" for the first element if only one is present.
- Second element ends with -ide.
Acids Naming
Binary Acids (Hydrogen + Nonmetal)
- Naming: Hydro+[nonmetal base]+ic acid (e.g., HCl = hydrochloric acid).
- Only two elements are present.
Oxyacids (Hydrogen + Polyatomic Ion)
- If the polyatomic ion ends in -ate: [base name]+ic acid (NO₃⁻ = nitric acid).
- If the polyatomic ion ends in -ite: [base name]+ous acid (NO₂⁻ = nitrous acid).
- Do not use the "hydro" prefix for oxyacids.
Formula Mass Calculations
- Formula mass = Σ(number of atoms × atomic mass for each element).
- Example: H₂O = (2×1.008) + (1×15.999) = 18.01 amu.
Key Terms & Definitions
- Ionic compound — compound of metal and non-metal ions.
- Molecular (covalent) compound — compound of only non-metals.
- Polyatomic ion — an ion composed of multiple atoms.
- Binary compound — compound with two elements.
- Binary acid — acid with hydrogen and one non-metal.
- Oxyacid — acid with hydrogen and a polyatomic ion containing oxygen.
- Formula mass — the sum of the atomic masses in a formula unit (amu).
Action Items / Next Steps
- Memorize common polyatomic ions and prefixes for molecular naming.
- Practice naming and writing formulas for each compound type.
- Complete any assigned reading or practice problems from chapter five.