​Aufbau Diagram - know this!

​What this tells you:

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​1. which energy levels hold which sublevels

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​2. the filling order for electron configurations. lowest energy 1s gets filled first.

​Pauli Exclusion Principle

​An atomic orbital may contain at most 2 electrons

• To occupy the same orbital the electrons must have an opposite spin (clockwise or counterclockwise)

• Use arrows to designate its spin 🡹🡻

​Hund's Rule

• One electron enters each orbital until all the orbitals contain one electron with the same spin direction

• Electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible.​

​Steps for Writing Electron Configurations

1. Analyze – Identify the relevant concepts, atomic number/number of electrons (i.e. Phosphorous – 15 electrons)

2. Place electrons in the orbital with the lowest energy first (1s), then continue placing electrons in each orbital with the next higher energy. (1s²2s²2p⁶3s²3p³)

3. The superscripts should add up to the number of electrons. ​

​Orbital Filling Diagrams

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​Abbreviated Electron Configurations

• ​Let's try Zirconium