Understanding Light, Atomic Models, and Quantum Mechanics
Nature of Light
Early Theories: Newton proposed that light consists of particles (corpuscular nature), while Huygens suggested a wave-like nature. Young demonstrated that light could be diffracted.
Wave Definition
A wave is the propagation of a vibrational disturbance that transmits energy, but not matter. Any wave is characterized by its amplitude, frequency, and wavelength.
Maxwell’s Electromagnetic Theory
Maxwell’s theory considers light as an electromagnetic wave, a non-material entity. The electromagnetic spectrum encompasses all wavelengths of electromagnetic radiation, with visible light occupying a small portion.
Bohr’s Atomic Model
Background
The Rutherford model, which preceded Bohr’s, provided evidence against the Thomson model. Rutherford’s experiments on alpha-ray scattering by thin metal foils indicated a nuclear structure for the atom. However, the Rutherford model had two main drawbacks:
- An electrically charged body in accelerated motion would release energy, causing the electron to spiral into the nucleus.
- The model could not explain atomic spectra.
Bohr proposed a new atomic model combining classical and quantum aspects.
Bohr’s Postulates
- Electrons orbit the nucleus only in specific, allowed fixed orbits called stationary states, which can absorb or emit energy.
- Only stationary states with angular momentum (L) that is an integer multiple of h/2π are acceptable.
- Electrons can jump between allowed orbits, absorbing or emitting energy. The frequency of the radiation satisfies the Planck quantum condition: ΔE = h · f.
Development and Limitations of the Bohr Model
Strengths
- Justified the stability of the atom through stationary orbits.
- Introduced the concept of energy levels.
- Explained atomic spectra and the hydrogen spectrum through atomic jumps.
- Related chemical properties to electronic structure.
Weaknesses
- Numerical results for polyhedral atoms did not match experimental values.
- Lacked coherence in its development.
Quantum Mechanics
Wave-Particle Duality for Matter
L. De Broglie proposed that if light exhibits both wave and particle properties, then other particles could also have wave-like properties. He reasoned that an electron bound to the nucleus behaves as a wave.
Schrödinger Equation
An atomic orbital is a region of space where there is a high probability of finding an electron. The square of the wave function in a given region indicates the probability of finding the particle in that region.
Uncertainty Principle
It is impossible to simultaneously determine with certainty both the position (x) and momentum (p = m · v) of a particle.