Does an atom look more like a solar system or a cloud? Learn how the early atomic theory has evolved into the modern atomic theory and changed the way science views the atom. Learn about contributions from Schrodinger and Heisenberg.

Atoms

When you think of an atom, you might picture a little solar system-like model with paths of electrons orbiting a centralized nucleus. This is the early atomic model that Niels Bohr and other scientific pioneers envisioned many years ago. But thanks to experimental advancements and some modern-day thinkers, like Erwin Schrodinger and Werner Heisenberg, we now believe that electrons look more like clouds than neatly orbiting planets. This new idea of what atoms look like is the basis of the modern atomic theory. Let’s take a look at how science advanced from its early understanding of atoms to the modern view of today.

Atomic Theory

Scientists have known about atoms long before they could produce images of them with powerful magnifying tools. In fact, atoms get their name from the Ancient Greek word atomos, which means ‘something that is not able to be divided’.

Because atoms could not be seen, the early ideas about atoms were mostly founded in philosophical and religion-based reasoning. Near the end of the 18th century, new ways to conduct experiments helped researchers build their scientific understanding of atoms. This lead to the first atomic theory, which stated things like, all matter is made up of atoms, elements are composed of only one type of atom, and atoms can combine with other atoms to make more complex substances.

This first atomic theory explained a lot, but as science continued to advance, new information and new discoveries made it clear that the theory needed to be updated. One of these new discoveries came at the end of the 19th century, with the discovery of a subatomic particle, called an electron. The word ‘subatomic’ literally means ‘inside an atom’. Because of this discovery it became clear that atoms might not have been named correctly and that they could be divided into smaller parts.

When electrons were first discovered, scientists knew they were part of the atom, but they didn’t know where they belonged. At first the thought was that electrons floated throughout the atom, like pieces of fruit floating in pudding, as if the atoms were simply soft blobs of matter. But, through more experimentation, it was found that most of the matter within atoms is centralized. By the early 20th century, this centralized matter came to be recognized as the nucleus of the atom.

The Bohr Model

In 1913, a scientist by the name of Niels Bohr expanded on all of the past research about atoms, and came up with the idea that negatively charged electrons orbit a positively charged nucleus in definite paths. This concept came to be known as the Bohr model. This was the first real look at the solar system-like model of an atom that we mentioned at the beginning of this lesson.

Schrodinger & Heisenberg

Bohr’s model was a big step forward in our understanding of the atom, yet it was still relatively simple and did not fully explain the nature of complex atoms that contained many electrons. This more complex understanding took shape thanks to the work of two 20th century scientists: Erwin Schrodinger and Werner Heisenberg.

Schrodinger became intrigued by the idea that electrons might move more like waves than particles. His ideas explained a lot about the nature of electrons and how they move; but it also created a problem for scientists.

Heisenberg and other scientists realized that if an electron moved as a wave, it would be impossible to simultaneously measure both its position and momentum. This became known as Heisenberg’s uncertainty principle. In other words, the exact path of an electron could not be predicted as Niels Bohr had predicted with the solar system model.

Modern Atomic Theory

Schrodinger and Heisenberg’s work lead to the modern atomic theory, which shows us that regions exist within an atom where electrons are likely to exist. These electron-containing regions that exist around the nucleus are referred to as electron clouds or orbitals. Electron clouds surround the nucleus and exist at different energy levels. An electron can exist at any distance from the nucleus; however, depending on its energy level, there are certain clouds that it will more probably, or more likely, be found in.

Lesson Summary

Let’s review. The Bohr model describes an atom that looks like a miniature solar system with negatively charged electrons orbiting a positively charged nucleus in definite paths.

Two 20th century scientists, Erwin Schrodinger and Werner Heisenberg, showed that this was not completely correct. Schrodinger explored the idea that electrons move more like waves than particles. His ideas led Heisenberg to develop the uncertainty principle, which states that if an electron moved as a wave, it would be impossible to simultaneously measure both its position and momentum.

Schrodinger and Heisenberg’s work led to the modern atomic theory, which shows us that regions exist within an atom where electrons are likely to exist. These electron-containing regions that exist around the nucleus are referred to as electron clouds or orbitals.

Learning Outcomes

When you are finished, you should be able to:

  • Describe and compare early atomic theory to modern atomic theory
  • Characterize the Bohr model
  • Discuss how the uncertainty principle proved the Bohr model wrong