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Electron Cloud: Definition, Model & Theory

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  • 0:02 Definition
  • 0:42 Model
  • 1:21 Theory
  • 3:14 Lesson Summary
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Lesson Transcript
Instructor: Elizabeth (Nikki) Wyman

Nikki has a master's degree in teaching chemistry and has taught high school chemistry, biology and astronomy.

Like the rapidly moving blades of a fan, electrons appear to occupy all of the space in an atom at once. Learn how electron location in an atom is best described by the electron cloud model and theory.

Definition

More often than not, when people visualize an atom they think of a small, positively charged nucleus being orbited by negatively charged electrons traveling in predictable paths. Unfortunately, electron movement is much more complicated than this.

As far as we know, electrons swarm around the nucleus of an atom in a mostly unpredictable fashion. At best, scientists can make guesses about where electrons are likely to be at any given time. Erratic electron behavior is best described by the electron cloud model. By definition, the electron cloud is the area around the nucleus of an atom where electrons are most likely to be found.

Model

This image depicts a helium atom on the atomic level. At the center is the nucleus, which consists of two protons and two neutrons. It is very small, only a billionth of a millimeter. Surrounding the nucleus is the electron cloud, a spherical shape that extends in all three dimensions from the nucleus.

You'll notice that the electron cloud is not evenly colored; it's darkest at the nucleus and gradually gets lighter as you travel away. This color gradient is based on electron probability, the likelihood of finding an electron in a certain location. Generally speaking, the chances of finding an electron decrease as you get farther away from the nucleus.

Theory

Since John Dalton breathed life into the atomic model in the early 1800s, scientists have been laboring to understand the intricacies of atomic structure. In the mid-1920s, research supporting the electron cloud model began to gain momentum as classical physics failed to explain such phenomena as how electrons could seemingly be everywhere at once, or why electrons did not crash into the nucleus when they gained or lost energy.

Research done by Max Planck, Albert Einstein and Niels Bohr unlocked some unexpected properties of light and energy: light is composed of discrete packets of energy called quanta, and energy behaves like both a particle and a wave. Electrons are transmitters of energy, so their properties are inextricably linked to that of light and energy. The behavior of energy and electrons on the atomic level were named quantum mechanics after the smallest unit of energy, a quantum.

In later years, the physicists Erwin Schrodinger, Werner Heisenberg and Louis de Broglie pioneered efforts to understand and describe electron behavior. Werner Heisenberg famously showed in the Heisenberg uncertainty principle that it is impossible to know both the location and speed of an electron at the same time. Building on de Broglie's theory that matter could exhibit wave-like properties, Schrodinger developed the concept of a wave function, a function that gives probable locations for an electron given the electron's total energy. When compiled, data from Schrodinger's equations can be used to create an electron probability diagram or the electron cloud for a specific atom.

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