# Electron Cloud Model: Theory, Explanation, and Creators

## 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.

## 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

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.

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

## 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.

In 1926, Schrodinger developed his wavefunction model, giving a probability for an electron to be in a particular location. He wrote to Albert Einstein in April of 1926, "This whole conception falls entirely within the framework of *wave mechanics*." Schrodinger's wavefunction was especially exciting to the physics community at large because it complemented Heisenberg's then-new mathematics for determining the position and energy of quantum particles, rather than correcting or refuting it.

Schrodinger created the electron cloud model to explain certain unknowns in quantum physics, but he knew that it didn't explain everything. He did not like this his equation did not directly describe the properties of a particle, and that it didn't really even define what a wave function was. The electron cloud model was built as a compromise, leaving some unknowns but erasing some others. In time, perhaps a better model will emerge.

### Heisenberg's Uncertainty Principle

In 1927, Heisenberg realized that there was an inherent uncertainty when measuring quantum particles. His thought experiment described an attempt to measure the position of a very small particle with a microscope. For an observer to do that, light would have bounce off of the quantum particle, but that photon of light would be enough to change the direction of a particle that small. This would mean that its direction or momentum would now be off, and the observer wouldn't know by precisely how much. More precise measurements of a quantum particle's position would require a stronger microscope, meaning higher-energy photons, meaning more uncertainty about the particle's momentum after the observation. Heisenberg realized that this was an essential component of quantum physics, not a limitation.

From there, he calculated that the product of the uncertainties of a particle's position and momentum has a minimum value (one half of Planck's Constant). As one gets smaller, the other gets larger, and neither can ever be zero.

### Schrodinger's Wave Function

Schrodinger developed the idea of the wave function in early 1926. Schrodinger's equation contains information about a particle's position, energy, and other properties, but it doesn't actually give values for them. Schrodinger's equation results in complex numbers (that have the imaginary number *i* included), but squaring them basically results in a probability distribution for the particle.

## Lesson Summary

An **electron** is a subatomic particle that, along with protons and neutrons, makes up an atom. Electrons are negatively charged, and their mass is very small, around {eq}9.1094 \cdot 10^{-31}\: kg {/eq}. The exact position of an electron cannot be known. Instead, we can calculate the probability that an electron is in a specific area. That area of interest is called the **electron cloud**. Inside this cloud, we can calculate where the electron "probably" is. A good visual example of an electron cloud is a simple atom, like Hydrogen. In a Hydrogen atom, the nucleus consists of one proton, and one electron orbits it. But the electron doesn't literally orbit it in a circular path. Instead, there is a cloud of possible locations for the electron, and that cloud is thicker where the probability is greater. In a Hydrogen atom, that cloud is a sphere around the nucleus that thins as it gets further out.

Erwin Schrodinger formulated the electron cloud model, building upon the work of many other physicists, such as Louis de Broglie, Albert Einstein, Neils Bohr, Max Planck, Werner Heisenberg, and many others. Heisenberg's Uncertainty Principle in particular necessitates something like an electron cloud, as it says that the position and momentum of a particle can not be known exactly. With very small particles, electrons included, classical physics concepts and equations no longer work very well. Named after **quanta**, the smallest possible unit of light, **quantum physics** deals with the unique and often counter-intuitive, behavior of small particles. Schrodinger's equation allows us to treat an electron as a **wave function**, which is essentially a complicated number that describes the properties of a particle, and helps create its probability field.

## 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 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.

The electron cloud model was created as a compromise between what physicists did understand about electron behavior and what they didn't understand. Perhaps a more concrete model of electron behavior will emerge as physicists continue to explore the quantum world.

## Lesson Summary

An **electron cloud** represents the area around an atom's nucleus where electrons are most likely to be found. It is a sphere that surrounds the microscopic nucleus, although it is often rendered as a ring in two-dimensional pictures. The cloud is darkest at the nucleus and lighter farther away, representing that electrons are more likely to be found closer to the nucleus than away from it.

**Quantum mechanics**, the science explaining how electrons move within atoms, was developed from the work of physicists such as Max Planck, Albert Einstein and Niels Bohr who found that light was made up of discrete energy packets, called quanta, which behaved both like a particle and a wave.

Building on the work of physicists Louis de Broglie and Werner Heisenberg, Erwin Schrodinger developed equations that gave probable locations for electrons according to their energy level. These equations, applied to every electron orbiting the nucleus, produce the shape of the electron cloud.

## Highlighted Terminology

Electron cloud |
the area around the nucleus of an atom where electrons are most likely to be found |

Electron probability |
the likelihood of finding an electron in a certain location |

Quanta |
discrete packets of energy |

Quantum mechanics |
behavior of energy and electrons at the atomic level |

Heisenberg uncertainty principle |
Heisenberg theorized that it is impossible to know both the location and speed of an electron at the same time |

Wave function |
function that gives probable locations for an electron given the electron's total energy |

## Learning Outcomes

Progress through this lesson at your own pace, then attempt to:

- Define an electron cloud and characterize its appearance
- Name some of the famous scientists who studied this phenomenon
- Recognize the meaning of the term 'quantum mechanics'

To unlock this lesson you must be a Study.com Member.

Create your account

## 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 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.

The electron cloud model was created as a compromise between what physicists did understand about electron behavior and what they didn't understand. Perhaps a more concrete model of electron behavior will emerge as physicists continue to explore the quantum world.

## Lesson Summary

An **electron cloud** represents the area around an atom's nucleus where electrons are most likely to be found. It is a sphere that surrounds the microscopic nucleus, although it is often rendered as a ring in two-dimensional pictures. The cloud is darkest at the nucleus and lighter farther away, representing that electrons are more likely to be found closer to the nucleus than away from it.

**Quantum mechanics**, the science explaining how electrons move within atoms, was developed from the work of physicists such as Max Planck, Albert Einstein and Niels Bohr who found that light was made up of discrete energy packets, called quanta, which behaved both like a particle and a wave.

Building on the work of physicists Louis de Broglie and Werner Heisenberg, Erwin Schrodinger developed equations that gave probable locations for electrons according to their energy level. These equations, applied to every electron orbiting the nucleus, produce the shape of the electron cloud.

## Highlighted Terminology

Electron cloud |
the area around the nucleus of an atom where electrons are most likely to be found |

Electron probability |
the likelihood of finding an electron in a certain location |

Quanta |
discrete packets of energy |

Quantum mechanics |
behavior of energy and electrons at the atomic level |

Heisenberg uncertainty principle |
Heisenberg theorized that it is impossible to know both the location and speed of an electron at the same time |

Wave function |
function that gives probable locations for an electron given the electron's total energy |

## Learning Outcomes

Progress through this lesson at your own pace, then attempt to:

- Define an electron cloud and characterize its appearance
- Name some of the famous scientists who studied this phenomenon
- Recognize the meaning of the term 'quantum mechanics'

To unlock this lesson you must be a Study.com Member.

Create your account

#### 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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