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# Pauli Exclusion Principle

## Spin differentiates electrons within the same orbital

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Pauli Must be Excluded

### What is the Pauli Exclusion Principle?

Is this principle simply another concept to memorize or something you have been familiar with since you were a kid? Go back in time to your younger childhood days and reminisce in melancholy. Does playing hide-and-seek with your friends strike importance? Go back to one of your plethora of hide-and-seek games, when you were one of the many hiders against the single seeker. You are in the park and the countdown of 100 begins. The adrenaline rushes through your veins as your friends take the best hiding spots: under the slide, behind the tree, and inside the playground fort. You find a decent spot: a small cylindrical, dark tunnel. But inside, you see your friend, already hiding there, who exclaims to you, “Pauli, you must be excluded!” Because your friend has taken this tunnel, you are not allowed to occupy the same hiding position. These hiding spots in which only a single person is entitled to are similar to quantum numbers.

Credit: Sam Howzit
Source: http://www.flickr.com/photos/aloha75/8623846009/lightbox/

[Figure1]

Electrons cannot occupy the same four quantum numbers. In one orbital, a maximum of two electrons can take position;  consequently, they must have different spin states (one would be up +12\begin{align*}\frac{1}{2}\end{align*} and the other would be down -12\begin{align*}\frac{1}{2}\end{align*}). This demonstrates how the quantum numbers, spin states, and configurations or directions of the electrons are not identical.

### Creative Applications

1. In the scenario of the visual concept, what do you and your friends represent?
2. What do the hiding places represent and why can each place only give shelter to a single person?
3. Would the game of hide-and-seek work well if a number of people can occupy the same hiding spot? How can you apply this with the Pauli Exclusion principle?

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