Overview
This lecture covers the models of atomic structure, detailing energy levels, sub-levels, orbitals, electron configurations, and how ions form by the loss or gain of electrons.
Models of the Atom
- The Bohr model describes electrons in fixed shells (energy levels) with specific capacities (2, 8, etc.).
- Early models predicted noble gas electron arrangements are stable for atoms and ions.
The A-Level Model of Electron Structure
- Principal energy levels are numbered with 1 closest to the nucleus.
- Each level has sub-energy levels: s, p, d, and f.
- s sub-level holds 2 electrons, p holds 6, d holds 10, f holds 14.
- Sub-levels contain orbitals, each holding up to 2 electrons with opposite spins.
- Orbitals represent probability regions for finding electrons and have specific shapes (s: spherical, p: dumbbell).
Order of Filling and Electron Configuration
- Sub-shells fill in order of increasing energy: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p, etc.
- 4s is filled before 3d due to its lower energy.
- Electron configuration notation uses numbers and letters (e.g., Oxygen: 1s² 2s² 2p⁴).
- For spin diagrams, each orbital is represented by a box with arrows for electrons (opposite spins).
Periodic Table Blocks and Electron Filling
- The periodic table is divided into s, p, d, and f blocks based on where outer electrons are filling.
- s-block elements have their outermost electron in an s-sub shell.
- When filling orbitals of a sub-level, each orbital gets one electron before any are paired.
Electronic Structure of Ions
- Positive ions form when electrons are lost (e.g., Mg: 1s² 2s² 2p⁶ 3s², Mg²⁺: 1s² 2s² 2p⁶).
- Negative ions form when electrons are gained (e.g., O: 1s² 2s² 2p⁴, O²⁻: 1s² 2s² 2p⁶).
Key Terms & Definitions
- Principal energy level — major shell around the nucleus, numbered 1, 2, 3, etc.
- Sub-level (s, p, d, f) — categories within energy levels with specific electron capacities.
- Orbital — region within a sub-level where up to 2 electrons with opposite spins are likely to be found.
- Spin — intrinsic property of electrons, with two possible orientations (up or down).
- Electron configuration — notation showing how electrons occupy energy levels and sub-levels in an atom or ion.
Action Items / Next Steps
- Practice writing electron configurations for various elements and ions.
- Review the order of filling sub-levels and corresponding positions on the periodic table.