Overview
This lecture introduces chemical bonding, focusing on covalent bonds and Lewis dot diagrams, and explains how valence electrons determine atom interactions and compound formation.
Chemical Bonding Fundamentals
- Chemical bonds form when atoms join to create new compounds.
- Bonds involve the interaction of valence electrons (outer shell electrons).
- The octet rule states atoms aim for eight valence electrons, except hydrogen (which aims for two).
- Atoms can gain, lose, or share electrons to achieve noble gas configurations.
Valence Electrons and the Periodic Table
- Main group elements in the periodic table have predictable numbers of valence electrons based on their group.
- Columns from left to right: 1–8 valence electrons, ignoring transition metals for basic chemistry.
- The goal for most atoms is to achieve the electron configuration of the nearest noble gas.
- Atoms on the left usually lose electrons; those on the right usually gain or share electrons.
Electron Configuration Review
- Valence electrons are those in the highest energy shell (largest n value).
- Example: Fluorine has 1s² 2s² 2p⁵; seven valence electrons are in the n=2 shell.
- Carbon: four valence electrons in 2s and 2p orbitals.
- Aluminum: three valence electrons in the n=3 shell.
Lewis Dot Diagrams
- Lewis dot diagrams show only valence electrons as dots around the element symbol.
- One dot per valence electron; up to two dots per side (around four sides).
- Examples: H (1 dot), He (2 dots paired), Li (1 dot), Be (2 dots), B (3 dots), C (4 dots), N (5 dots), O (6 dots), F (7 dots), Ne (8 dots).
- Group elements in the same column have similar dot diagrams due to the same number of valence electrons.
Ions and Lewis Dot Diagrams
- Cations (positive ions) lose electrons; their diagrams have fewer dots than the neutral atom.
- Anions (negative ions) gain electrons; their diagrams have more dots than the neutral atom.
- For cations: use only the symbol and charge (no dots for full shell).
- For anions: fill out the octet with eight dots around the symbol.
Special Cases and Limitations
- Transition metals: typically omit d and f electrons in Lewis diagrams; focus on main group elements.
- Only responsible for dot diagrams of main group elements, not transition metals, in introductory chemistry.
Key Terms & Definitions
- Valence Electrons — electrons in the outermost shell, responsible for bonding.
- Octet Rule — tendency of atoms to have eight electrons in their valence shell.
- Lewis Dot Diagram — graphical representation of an atom’s valence electrons as dots around its symbol.
- Cation — positively charged ion formed by losing electrons.
- Anion — negatively charged ion formed by gaining electrons.
- Core Electrons — non-valence electrons; not shown in Lewis diagrams.
Action Items / Next Steps
- Practice drawing Lewis dot diagrams for main group elements and simple ions.
- Review electron configurations for identifying valence electrons.
- Familiarize yourself with group numbers and valence counts on the periodic table.