Lecture Notes: Electron Configurations and D Orbitals

Overview

Discussion of electron configurations for potassium, calcium, and their ions, followed by scandium and other transition metals.
Focus on noble gas notation and changes in energy levels in d orbitals.

Potassium (K)
- Located in the fourth period of the periodic table.
- Uses noble gas notation: Argon [Ar] in brackets.
- Potassium has 19 electrons, one more than Argon.
- Electron configuration: [Ar] 4s¹.
Calcium (Ca)
- One more electron than potassium.
- Electron configuration: [Ar] 4s².
- Formation of calcium ion (Ca²⁺) involves losing two 4s electrons, resulting in [Ar] configuration.

Scandium (Sc)
- One more electron than calcium.
- Expected configuration might seem like [Ar] 3d³, but actual configuration is [Ar] 4s² 3d¹.
- Key Concept: Energy level anomaly where 4s is higher than 3d due to factors like nuclear charge.
- Known from ionization experiments indicating the 4s orbital loses electrons first.

General Strategy: Use noble gas notation, followed by counting orbitals based on their order on the periodic table.
Titanium (Ti)
- [Ar] 4s² 3d².
- Implies filling of d orbitals after the 4s even though in reality, 4s is higher in energy.
Vanadium (V)
- Follows Hund's rule; fills unpaired first.
- Configuration: [Ar] 4s² 3d³.
Chromium (Cr)
- Expected: [Ar] 4s² 3d⁴.
- Actual: [Ar] 4s¹ 3d⁵.
- Explanation involves half-filled d subshell stability.
Manganese (Mn) to Zinc (Zn)
- Manganese (Mn): [Ar] 4s² 3d⁵.
- Iron (Fe): [Ar] 4s² 3d⁶.
- Cobalt (Co): [Ar] 4s² 3d⁷.
- Nickel (Ni): [Ar] 4s² 3d⁸.
- Copper (Cu): [Ar] 4s¹ 3d¹⁰.
- Zinc (Zn): [Ar] 4s² 3d¹⁰.

Writing configurations involves both the correct sequence and understanding energy changes.
Real-world electron behavior isn't always intuitive and can be complex.
Orbital filling rules (like Hund's rule) and exceptions (as seen with chromium and copper) need careful consideration.