Lecture on Electrons and Electron Configuration

Introduction to Electrons

• Electrons are fundamental particles.
• Mass of an electron: 9.11 x 10^-31 kg.
• Charge: negative.
• Understanding electrons is crucial for chemistry.
• Atoms behave based on their electron relationships.

Electron Behavior and Bonding

• Atoms change electron numbers for stability.
• Can form ions by stealing electrons, leading to ionic bonds.
• Can share electrons to form covalent bonds.

Electron Location and Orbitals

• Electrons exist outside the nucleus.
• More likely to be found in certain areas, forming electron orbitals.
• Orbitals have defined shapes: s, p, d, f.

Electron Spin and the Pauli Exclusion Principle

• Spin describes angular momentum; no macroscopic counterpart.
• Electrons have "up" or "down" spin.
• Orbitals can hold two electrons with opposite spins.
• Pauli Exclusion Principle: No two electrons can occupy the same state in an atom.

Electron Shells and Orbitals

• Electrons organized in shells based on energy, indicated by principal quantum number (n).
• Types of orbitals:
  • s orbital: Spherically shaped, one per shell.
  • p orbital: Dumbbell-shaped, three per shell.
  • d orbital: Mostly clover-shaped, five per shell.
  • f orbital: Uniquely shaped, seven per shell.
• Groups of orbitals with the same energy are called subshells.

Counting Orbitals

• Shell 1: 1s orbital.
• Shell 2: 2s and 3 p orbitals (total 4 orbitals).
• Shell 3: 3s, 3p, and 5 d orbitals (total 9 orbitals).
• Number of orbitals in a shell = n^2.

Electron Configuration Guidelines

1. Aufbau Principle: Electrons fill orbitals from lowest to highest energy.
2. Pauli Exclusion Principle (mentioned above).
3. Hund's Rule: Electrons fill separate orbitals with same spin before pairing.

Electron Configurations

• Arrangement of electrons in an atom.
• Shows shells and subshells order by increasing number and energy.
• Example: Nitrogen (7 electrons) has configuration 1s² 2s² 2p³.
• Ion formation: Atoms gain/lose electrons, forming ions.

Noble Gas Configuration

• Inner shells often match noble gas configurations.
• Example: Phosphorus uses neon configuration as a base.

Exceptions in Electron Filling

• 3d and 4s subshells: Can fill in different orders due to energy similarities.
• Example: Chromium ends in 4s¹ 3d⁵ instead of 4s² 3d⁴.
• Copper ends in 4s¹ 3d¹⁰ instead of 4s² 3d⁹.

Conclusion

• Electron behavior is fundamental to chemistry.
• Different models offer insights into electron behavior and atomic interactions.