Stability of Atoms in Quantum Chemistry
Classical physics could not explain why atoms are stable. According to classical ideas:
- An electron orbiting a nucleus should continuously lose energy as radiation.
- It would spiral into the nucleus → atom should collapse.
- But in reality, atoms are stable → so a new explanation was needed.
Quantum chemistry provides that explanation through the following ideas:
1. Quantized Energy Levels
- Electrons can only exist in fixed, discrete energy levels (orbitals) around the nucleus.
- They cannot occupy energies in between or spiral down gradually.
- The lowest energy state (called the ground state) is stable because there’s no lower energy level to fall into.
2. Wave Nature of Electrons (de Broglie)
- Electrons behave like standing waves around the nucleus.
- Only wave patterns that “fit” the atom are allowed → stable orbitals form.
- This prevents electrons from crashing into the nucleus.
3. Schrödinger Equation & Orbitals
- Quantum chemistry solves Schrödinger’s equation for the hydrogen atom → gives orbitals with specific shapes (s, p, d, f) and energies.
- Electrons in these orbitals have defined probabilities of being near the nucleus, not a collapsing spiral.
4. Pauli Exclusion Principle
- No two electrons in an atom can have the same set of quantum numbers.
- This spreads electrons into different orbitals and energy levels.
- It explains electron configuration and the stable structure of atoms.
5. Balance of Forces
- Electrostatic attraction pulls electrons toward the nucleus.
- Quantum mechanical effects (wave nature + exclusion principle) push back, preventing collapse.
- This balance explains why atoms have a definite size and remain stable.
In short:
Quantum chemistry explains atomic stability because electrons can only exist in specific quantized states (orbitals). They cannot lose energy continuously and collapse into the nucleus. The combination of quantized energy levels, wave-like behavior, and the Pauli principle keeps atoms stable and gives rise to the structure of the periodic table.