# What is a Wave-Mechanical Model?

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Lesson Transcript
Instructor: Michael Quist

Michael has taught college-level mathematics and sociology; high school math, history, science, and speech/drama; and has a doctorate in education.

When scientists realized that electrons around the nucleus of an atom don't really behave like planets around the sun, they had to propose a new model. This lesson will discuss the wave-mechanical model of the structure of an atom.

## Wave-Mechanical Models

Electrons race around a central nucleus at such high speeds, that they act like waves of energy.

As electrons push each other around, the electron orbital clouds form different shapes. Scientists propose that atoms can have up to seven principle energy levels of electrons around the nucleus.

This is the electron configuration for the element sulfur, which has 16 electrons.

We and everything around us are made of tiny groups of particles, called atoms. While atoms were once thought to be the smallest unit of matter, they are actually made up of much tinier, high-energy, negatively-charged particles circling at a crazy pace around a nucleus of positive and neutral particles. Since the outer-shell (valence) electrons control the chemical properties of a material, it would be useful to understand how they behave.

One popular theory is the wave-mechanical model, which proposes that electrons are almost as much like a wave of energy as they are like particles. They're moving so fast that they're not really in any one place at any given time, and they keep changing their path in response to the fields around them. In this lesson, we will discuss how scientists use the wave-mechanical model to describe the construction of an atom.

The wave-mechanical model was proposed in the 1920s when scientists Erwin Schrödinger and Louis Victor de Broglie determined that the previous model (the Bohr model) was not useful for determining electron locations. The wave-mechanical theory proposes that each electron circling an atom's nucleus occupies a specific orbital and spins a certain direction, but the orbital is like a cloud or wave of energy, not the ring you might imagine thinking about the earth's orbit around the sun.

## Fundamentals

As scientists have studied the structure of the atom, they have found that they must assume the following things:

1. Scientists cannot ever know exactly how electrons move around the nucleus of an atom (this is related to the uncertainty principle).
2. If scientists take a 'snapshot' in time, they can identify certain areas where electrons are more likely to be than others (this is related to the probability model).
3. If scientists accumulate the 'snapshots,' they can make a 'probability map' that shows locations where the electron is more likely to be or less likely to be.
4. Electrons are in an orbital around their positively-charged nucleus, based on how fast they're moving, and that orbital can be defined by the 'probability map,' which helps to determine a 'shape' for each sub-shell.
5. Each orbital shell essentially contains 90% of the electron's paths and likely locations.

Using these assumptions, scientists began to map out their best guesses about the behavior of electrons at various energy levels around a nucleus. Since the electrons are all negatively charged, they tend to 'bump elbows' if they get too near to each other, pushing away and changing their direction of travel. Each sub-level has one or more orbitals containing one or two electrons that travel around the nucleus in a particular pattern, or shape.

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