Overview
This lecture introduces how to write electron configurations for atoms and ions, using examples like nitrogen, aluminum, iron(II), and the chloride ion.
Energy Levels and Sublevels
- Atoms have energy levels (shells) labeled 1, 2, 3, etc.
- Each energy level has sublevels: s, p, d, and f (increasing in higher levels).
- s sublevel holds up to 2 electrons, p holds 6, d holds 10, f holds 14.
Writing Electron Configurations for Atoms
- Use the atomic number to determine the number of electrons in a neutral atom.
- Fill electrons starting from 1s, proceeding through 2s, 2p, 3s, 3p, etc.
- Stop adding electrons once you reach the atom’s total electron count.
Example: Nitrogen (Atomic number 7)
- Configuration: 1s² 2s² 2p³ (2+2+3=7)
Example: Aluminum (Atomic number 13)
- Configuration: 1s² 2s² 2p⁶ 3s² 3p¹ (2+2+6+2+1=13)
Writing Electron Configurations for Ions
- For ions, adjust the number of electrons by the charge (add for negative, subtract for positive).
Example: Fe²⁺ (Iron, Atomic number 26, loses 2 electrons)
- Write neutral atom configuration first: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶.
- Remove electrons from the highest energy level (4s before 3d): resulting configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶.
Example: Chloride Ion (Cl⁻, Atomic number 17, gains 1 electron)
- Chloride ion has 18 electrons.
- Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶.
Special Notes on Transition Metals
- For transition metal ions, always remove electrons from the highest principal energy level first (typically s before d).
- It’s best to write the neutral atom's configuration, then subtract electrons as needed.
Key Terms & Definitions
- Electron Configuration — shorthand notation showing electron placement in energy levels and sublevels.
- Sublevel — subshell within an energy level (s, p, d, f).
- Transition Metal — elements in the d-block of the periodic table.
- Ion — atom with a net positive or negative charge due to loss or gain of electrons.
Action Items / Next Steps
- Practice writing electron configurations for other main group and transition metal ions.
- Review periodic table to identify sublevels for each energy level.