Overview
This lecture covers the differences between ionic and covalent bonds, their properties, naming rules for compounds, the concept of polyatomic ions, and key definitions.
Types of Chemical Bonds
- Ionic bonds form from electrostatic attraction between oppositely charged ions, usually a metal and a nonmetal.
- In ionic bonding, one atom donates electrons and another atom accepts, resulting in cations and anions.
- Ionic compounds generally have high melting/boiling points and conduct electricity when dissolved or molten.
- Covalent bonds involve the sharing of electrons between two nonmetals.
- Covalent compounds have lower melting/boiling points and do not conduct electricity in solution.
Key Definitions and Concepts
- Cations are positively charged ions formed by electron loss.
- Anions are negatively charged ions formed by electron gain.
- The octet rule states that atoms tend to achieve eight electrons in their outer shell for stability.
- Lewis structures are diagrams showing arrangement of electrons, helping visualize molecular geometry and bonding.
Naming Compounds
- Ionic compounds: named by stating the metal, then the nonmetal with an -ide suffix (e.g., sodium chloride).
- Transition metals in ionic compounds use Roman numerals to denote charge (e.g., iron(II) chloride).
- Covalent compounds: prefixes indicate number of each atom (e.g., carbon dioxide); “mono-” is omitted for the first element.
Special Types of Ions
- Polyatomic ions consist of two or more atoms bonded together, carrying a net charge (e.g., sulfate SO₄²⁻, ammonium NH₄⁺).
- Polyatomic ions participate in ionic bonding similarly to monatomic ions.
Common Compounds and Their Names
- Calcium chloride (CaCl₂) is an ionic compound of calcium ions and chloride ions.
- Water (H₂O) is a covalent compound where hydrogen and oxygen share electrons.
- Ammonia (NH₃) is a covalent compound of nitrogen and hydrogen atoms.
Key Terms & Definitions
- Ionic bond — attraction between oppositely charged ions.
- Covalent bond — sharing of electron pairs between atoms.
- Cation — positively charged ion.
- Anion — negatively charged ion.
- Octet rule — atoms seek eight valence electrons for stability.
- Polyatomic ion — charged species with two or more bonded atoms.
Action Items / Next Steps
- Review Lewis structures for predicting molecular geometry.
- Practice naming compounds with given formulas and vice versa.
- Memorize common polyatomic ions and their charges.