Atomic Models

Priya Vanparia & Amie Deng

Thales of Miletus

Scientist Background

  • Thales was a philosopher and he was one of the Seven Sages of Greece.

  • Pre-Socratic Greek philosopher

General Information

Dates of Importance:

  • 582 BC


  • Founder of school of natural philosophy; introduced mathematics and astronomy to the Greeks.

Philosophy and Contributions to Understanding the Atom:

  • Thales suggested that water was the basic substance from which the universe is composed and thought the earth floated on water. This is an incorrect hypothesis.

  • He was the first person to suggest that all matter was unified by a common building block.
Thales: Biography of a Great Thinker

Niels Bohr

Scientist Background

  • Copenhagen, Denmark

  • Bohr specialized in theoretical nuclear physics.

  • He won a Nobel prize regarding the structure of atoms.

  • Bohr's greatest contribution to modern physics and chemistry was the atomic model. The Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons.

  • Bohr was the first to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element.

  • Atomic model, quantum model, and liquid droplet theory

Important dates related to contribution of Atomic Theory

  • 1922: atomic model, Nobel Peace Prize

  • 1912: joined Rutherford

Key Points

  • He theorized that electrons occupy shells or energy levels.

  • Explained that elemental properties are related to occupancy of outermost electron shells.

  • Showed that electrons can jump to higher shells with light absorption and fall back to lower shells with light emission.

  • Win Nobel Peace prize for physics in 1922

Description of experimental design to understand the nuclear atom:

  • He developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of successive orbital shells of electrons.

The Bohr model depicts the atom as a small, positively-charged nucleus surrounded by negatively-charged electrons that travel in circular orbits around the nucleus, similar in structure to the Solar System, but with electromagnetic forces providing attraction, rather than gravity.

Procedures involved in the experiment:

  • When Bohr joined Rutherford, he realized that his model wasn't exactly right in which lead him to alter Rutherford's model and later published his own ideas in 1913.

  • He also took many notes, which ultimately lead to his development of the Bohr model and his other theories.

Data Collected

Bohr turned to Planck's quantum theory to explain the stability of most atoms. He found that the ratio of energy in electrons and the frequency of their orbits around the nucleus was equal to Planck's constant as he thought that Rutherford's model should be more unstable.

Analysis and Conclusions Drawn:

  • Electrons occupy only certain orbits around the nucleus. Those orbits are stable and are called "stationary" orbits. Electrons orbit the nucleus in discrete paths.

  • Each orbit has an energy associated with it. The orbit nearest the nucleus has an energy of E1, the next orbit E2, etc.

  • Energy is absorbed when an electron jumps from a lower orbit to a higher one and energy is emitted when an electron falls from a higher orbit to a lower orbit.

  • The energy and frequency of light emitted or absorbed can be calculated by using the difference between the two orbital energies.


Philosopher Thales and physicist Niels Bohr were researched in the context of their contributions towards the understanding of the atom. Minimal information was found regarding Thales as he existed in the ancient times of the world, though he implemented that the basic structure of all matter derived from the basic element of water. In contrast, much information was found on Bohr and he created the atomic model, liquid-droplet theory, and the quantum theory. Together, their augmentation aided and shaped chemistry into what it is today.

"Never express yourself more clearly than you are able to think."

Works Cited