Overview
This lecture covers how to name ionic compounds, including rules for naming cations and anions, determining charges, physical properties of ionic compounds, and naming compounds with polyatomic ions.
Naming Ionic Compounds
- Name the cation (positive ion) first, then the anion (negative ion).
- Main group cations (Groups 1, 2, 13, zinc, silver) use the element name without a charge or Roman numeral.
- Transition metals and other metals with variable charge require Roman numerals to indicate the charge (e.g., iron(II)).
- Nonmetals used as anions change the ending to "-ide" (e.g., chlorine becomes chloride).
Determining Ion Charges
- To name compounds with variable-charge metals, determine the charge by balancing total positive and negative charges to zero.
- Roman numerals represent the charge of the cation, not the number of atoms (e.g., copper(II) chloride for CuCl₂).
- Use the charges of known ions to deduce unknown charges in a compound.
Physical Properties of Ionic Compounds
- Ionic compounds have high melting and boiling points due to strong electrostatic attraction.
- Most dissolve well in water and dissociate into ions, forming electrolytes that conduct electricity.
Polyatomic Ions and Compound Naming
- Polyatomic ions are groups of atoms with an overall charge; memorize their names, formulas, and charges.
- When writing formulas, use parentheses around polyatomic ions if more than one is present (e.g., Mg(OH)₂).
- Do not alter the polyatomic ion’s name when naming compounds (e.g., sodium nitrate).
- Naming compounds: main group cation + polyatomic anion (no name change); transition metal cation + polyatomic anion (add Roman numeral).
Key Terms & Definitions
- Cation — Positively charged ion.
- Anion — Negatively charged ion.
- Main group cation — Ion from Groups 1, 2, 13, Zn²⁺, or Ag⁺; fixed charge, no Roman numeral.
- Transition metal cation — Metal ion with variable charge; requires Roman numeral to indicate charge.
- Polyatomic ion — Charged group of covalently bonded atoms.
- Electrolyte — Solution containing ions that conducts electricity.
Action Items / Next Steps
- Memorize polyatomic ions, their names, formulas, and charges.
- Practice writing and naming ionic compounds using the online quiz website.
- Focus on ionic compounds and polyatomic ions for current practice.
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Simple Notes on Naming Ionic Compounds
How to Name Ionic Compounds
- Name the positive ion (cation) first, then the negative ion (anion).
- For metals in groups 1, 2, 13, plus zinc and silver, just use the metal’s name (no numbers or extra info).
- For metals that can have different charges (like iron or copper), put a Roman numeral after the metal name to show the charge. For example, iron(II) means iron with a +2 charge.
- For nonmetals (negative ions), change the ending of the element name to "-ide." For example, chlorine becomes chloride.
Figuring Out Charges
- To name compounds with metals that have different charges, figure out the charge by making sure the total positive and negative charges balance to zero.
- The Roman numeral shows the charge of the metal ion, not how many atoms there are.
- Use what you know about the charges of other ions to figure out the unknown charge.
Properties of Ionic Compounds
- Ionic compounds have very high melting and boiling points because the positive and negative ions stick together strongly.
- Most ionic compounds dissolve in water and break apart into ions, which can carry electricity. These solutions are called electrolytes.
Polyatomic Ions (Groups of Atoms with Charge)
- Polyatomic ions are groups of atoms that act like one ion with a charge.
- You need to memorize their names, formulas, and charges.
- When writing formulas, if you have more than one polyatomic ion, put parentheses around it. For example, Mg(OH)₂ means two hydroxide ions.
- When naming compounds with polyatomic ions, don’t change the name of the polyatomic ion.
- For metals with variable charges plus polyatomic ions, still use Roman numerals for the metal charge.
Important Words
- Cation: Positive ion.
- Anion: Negative ion.
- Main group cation: Metals from groups 1, 2, 13, plus zinc and silver; always have the same charge.
- Transition metal cation: Metals that can have different charges; need Roman numerals.
- Polyatomic ion: Group of atoms with a charge.
- Electrolyte: A solution with ions that can conduct electricity.
What to Do Next
- Memorize the polyatomic ions.
- Practice naming and writing formulas for ionic compounds.
- Focus on ionic compounds and polyatomic ions for now.
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