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Electron Cloud Model: Theory, Explanation, and Creators

Ryan Johnson, Elizabeth (Nikki) Wyman
  • Author
    Ryan Johnson

    Ryan has tutored high school and college level math and science for over a decade, and has taught in a classroom setting for more than two. He has a BA in Chemistry from Ferris State University, and an MA in Archaeology from the University of Kansas.

  • Instructor
    Elizabeth (Nikki) Wyman

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

What is an electron cloud? Learn the definition of electron and electron cloud, learn about the electron cloud model, and view an electron cloud diagram. Updated: 09/08/2021

Definition of Electron

An electron is a subatomic particle, one of the three that make up atoms, and it carries a negative charge. It is also a charged lepton, because it carries a charge and has a half-integer spin. An electron is also an elementary particle, because it has no known substructure (other subatomic particles are made of smaller quarks). In an atom, electrons orbit the positively charged nucleus, which is made of protons and neutrons. Since protons are positively charged, electrons are attracted to the nucleus.

What is an Electron Cloud?

An electron cloud is the area of space in which an electron "probably is." This might seem like a rather odd concept, since we just described an electron as a particle. It seems like it would be in a particular location. This is not the case, however. An electron's true position in space is uncertain to a degree, and the electron cloud is the area of probability that exists for its location. The density of the cloud is proportional to the probability of an electron being there.

In an atom, the electron cloud surrounds the nucleus, and it is most dense near the nucleus. So instead of saying the electron is at a particular spot, we say that the electron is very likely to be in this zone, less likely to be in this zone, not very likely to be in this zone, and so on. The electron cloud has fuzzy edges, dissipating as it moves away from the nucleus. It doesn't really have an edge where it ends, but it does decrease in density very quickly as distance from the nucleus increases.

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.

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Electron Cloud Model: What Does the Electron Cloud Model Describe?

Let's look at a simple atom to see what the electron cloud model describes. A Hydrogen atom has one proton and one electron. A classic and probably more familiar model for the Hydrogen atom looks like this

The nucleus in red is a single proton, and the electron in yellow orbits it in a circular path.

diagram of electron orbiting nucleus

This model shows the path of the electron as a circle around the nucleus, orbiting it like the Moon orbits the Earth. This is not exactly incorrect; in fact, we say that the electron does orbit the nucleus. It is not a complete model, however, as it doesn't match all of our observations about how atoms and electrons behave. A better model views the electron's orbit as a cloud, where its position is uncertain and exists as a probability.

In the electron cloud model, the nucleus is still in the center, but the election does not have a set path around it.

diagram of electron cloud model of atom

The cloud is more dense near the nucleus, so there is a greater probability that the electron will be near there than anywhere else. Note that this model still has one proton and one electron in a Hydrogen atom. It also puts the electron on a path around the nucleus. The electron cloud model does two things that other models do not. It acknowledges the uncertainty of the electron's position, and it resolves some of that uncertainty for us. It matches more of our real world observations, things for which earlier models cannot account.

Electron Cloud Diagram

As shown here, the electron cloud is very close to the nucleus, and its probability field quickly fades.

accurate diagram of electron cloud model

Theories Behind the Electron Cloud Model

The electron cloud model is a combination of several different theories. First is Werner Heisenberg's Uncertainty Principle, which says that the momentum and position of a particle cannot both be known with arbitrary precision. That is, after a certain point, the more accurately we can measure one, the less we know about the other. Next, Erwin Schrodinger's concept of the wave function shows that we can treat every particle as a complicated value that describes its position and energy, and that can be interpreted as a probability. Both of these concepts fall under the umbrella of Quantum Physics, which had been developed previously by Albert Einstein, Niels Bohr, Max Planck, and others. Quantum Physics tells us that as particles get smaller, classical (Newtonian) physics gets less and less accurate in explaining their behavior. Beyond a threshold, quantum physics takes over completely. The word "quantum" refers to quanta, the smallest possible unit of energy or light.

Electrons are very small particles, having a mass of {eq}9.1094 \cdot 10^{-31}\: kg {/eq}, so their behavior is explained mostly by quantum physics. So for an electron, the uncertainty principle holds, and we can confidently treat it as a wave function. With the proper math, we can describe an electron's position as a probability field, normally distributed around the nucleus of an atom. The wave function of an electron also explains why the electron doesn't hang out in the nucleus. The energy needed to keep it there is too high.

Who Created the Electron Cloud Model?

Erwin Schrodinger came up with the model of the electron cloud, though he built upon previous work to develop of the theory. An early contributor was Louis de Broglie's idea that particle-wave duality applied to both light and particles of matter, allowing particles with mass, like electrons, to even have a wave function. Schrodinger also built upon Niels Bohr's model of the atom, which had electrons orbiting the nucleus in circular paths but also had them capable of being excited to higher energy levels.

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.

Helium atom

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 the 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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Video Transcript

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.

Helium atom

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 the 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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Frequently Asked Questions

Why is it called an electron cloud?

An electron cloud kind of looks like a cloud. It is thicker in the center and fades out at the edges. The term cloud also describes the many possible locations of the electron within a particular area. For an observer, the electron's position is more of a cloud than a single point.

Who came up with the electron cloud model?

Erwin Schrodinger came up with the electron cloud model, building on the work of several other physicists. Louis de Broglie's particle-wave duality particles with mass, Max Planck's and Albert Einstein's work with quantum physics, Neil Bohr's earlier model of the atom, Werner Heisenberg's Uncertainty Principle, and Schrodinger's wave function formula all contributed towards the concept of the electron cloud.

What best describes an electron cloud?

The electron cloud is a particular area in which an electron is likely to be. We can't say exactly where an electron is, but we can use its wave function to show the probability that it is in a particular area. That probability field is the called the electron cloud.

What is another name for an electron cloud?

An electron cloud can be thought of as a probability field, the area in space where an electron is likely to be. In an atom, these fields, specific regions of space where an electron most likely hangs out, are called orbitals.

Why is it called the electron cloud model?

The electron cloud model shows a particular area in which an electron is likely to be. In a simple atom like Helium for instance, the probability field is a sphere surrounding the nucleus, and the electron is more likely to be closer to the nucleus than far away from it. The probability field is denser in the middle and fizzles outward, and so it actually resembles the cloud of possible and probable locations for the electron.

What is the electron cloud model used for?

The electron cloud is used to describe the behavior of electrons, and it is useful in building a model of the atom. The electron cloud shows the area in space where an electron is most likely to be. The quantum behavior of electrons is useful in some technologies, such as very sensitive microscopes.

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