Atomic Models Explained: From Dalton to Bohr-Sommerfeld

Understanding Atomic Structure and Models

What is a Subatomic Particle?

A subatomic particle is a particle smaller than an atom. It can be an elementary particle or a composite particle, in turn, composed of other subatomic particles such as quarks, which make up protons and neutrons.

Dalton's Atomic Theory: Foundations of Chemistry

Key Postulates of Dalton's Theory

1. Elements are composed of tiny particles called atoms.
2. All atoms of a given element are identical in mass and properties.
3. Atoms of one element differ from those of any other element; atoms of different elements can be distinguished by their relative atomic weights.
4. Atoms of one element combine with atoms of other elements to form chemical compounds. A given compound always has the same relative number and types of atoms.
5. Atoms cannot be created or divided into smaller particles, nor destroyed in a chemical process. A chemical reaction simply rearranges how atoms are grouped together.

Rutherford's Atomic Model: The Nuclear Atom

Rutherford's model was the first atomic model which proposed that the atom consists of two parts: the electron cloud, consisting of all its electrons, spinning at high speed around a very small nucleus, which concentrates all the positive electric charge and almost all the mass of the atom.

Bohr's Atomic Model: Quantized Orbits

In the Bohr atomic model, electrons revolve in circular orbits around the nucleus, occupying the lowest possible energy orbit, or the orbit closest to the nucleus. Classical electromagnetism predicted that a charged particle moving in a circular orbit would emit energy, causing electrons to spiral into the nucleus instantaneously. To overcome this problem, Bohr assumed that electrons could only move in specific, quantized orbits, each characterized by its energy level. Each orbit is identified by an integer n (the principal quantum number), which takes values from 1 onwards.

The Bohr-Sommerfeld Model: Refining Energy Levels

The Bohr-Sommerfeld atomic model worked very well for the hydrogen atom. However, observations of spectra for atoms of other elements revealed that electrons within the same energy level exhibited slightly different energies, indicating a limitation in the model. It was concluded that within the same energy level, there existed sublevels, meaning slightly different energies.