The Aufbau Principle is an important rule that helps us understand how electrons are arranged in atoms.

This principle tells us that electrons will fill the lower energy levels first before moving to higher ones.

Order of Filling Energy Levels

Here’s the order in which electrons fill up the different energy levels, according to the Aufbau Principle:

1. 1s
2. 2s
3. 2p
4. 3s
5. 3p
6. 4s
7. 3d
8. 4p
9. 5s
10. 4d
11. 5p
12. 6s
13. 4f
14. 5d
15. 6p
16. 7s
17. 5f
18. 6d
19. 7p

How Many Electrons Can Each Orbital Hold

Each type of orbital can hold a different number of electrons:

• The s orbital can hold 2 electrons.
• The p orbital can hold 6 electrons.
• The d orbital can hold 10 electrons.
• The f orbital can hold 14 electrons.

Why This Matters for the Periodic Table

This way of filling orbitals helps explain how elements are placed in the periodic table and their chemical behaviors.

For example:

• Neon (Ne) has the electron arrangement of 1s² 2s² 2p⁶. This means its outer shell is full, making it stable and unreactive.
• Sodium (Na), on the other hand, has 1s² 2s² 2p⁶ 3s¹. This shows it has one extra electron, which makes it more likely to react with other elements.

Understanding these ideas is really important for knowing how elements behave during chemical reactions!