Overview
This lecture introduces how to write electron configurations for atoms and ions using examples like nitrogen, aluminum, iron, and chlorine.
Basics of Electron Configuration
- Electron configuration shows the arrangement of electrons in an atom's energy levels and sublevels.
- Atomic number equals the number of electrons in a neutral atom.
- Sublevels fill in the order: s (2 electrons), p (6), d (10), f (14).
- The filling order by energy levels: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, etc.
Example: Nitrogen (N)
- Nitrogen has 7 electrons (atomic number 7).
- Fill order: 1s² 2s² 2p³ (2 + 2 + 3 = 7).
Example: Aluminum (Al)
- Aluminum has 13 electrons.
- Fill order: 1s² 2s² 2p⁶ 3s² 3p¹ (2 + 2 + 6 + 2 + 1 = 13).
- Stop adding electrons once the total matches the atomic number.
Electron Configurations for Ions
- For positive ions (cations), subtract electrons equal to the charge.
- For negative ions (anions), add electrons equal to the charge.
- For non-transition metals, you can go straight to the ion's electron count.
- For transition metals, write the atom's configuration first, then remove electrons from the highest energy level.
Example: Iron (Fe and Fe²⁺)
- Iron atom (Fe): 26 electrons → 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶.
- Fe²⁺: Remove two electrons from the 4s sublevel → 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶.
Example: Chloride Ion (Cl⁻)
- Chlorine atom has 17 electrons; Cl⁻ has 18 electrons.
- Fill order for 18 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶.
- For Cl atom: 3p⁵, for Cl⁻: 3p⁶ (one extra electron).
Key Terms & Definitions
- Electron Configuration — the notation showing how electrons are distributed in an atom’s sublevels.
- Sublevel (s, p, d, f) — regions within energy levels where electrons reside, each with a maximum electron capacity.
- Cation — positively charged ion (fewer electrons than protons).
- Anion — negatively charged ion (more electrons than protons).
- Transition Metal — elements in the d-block which may lose s and sometimes d electrons first when ionized.
Action Items / Next Steps
- Practice writing electron configurations for sodium, magnesium, and copper.
- Review periodic table sublevel order for electron filling.
- Prepare for a quiz on electron configurations for ions and atoms.