The Aufbau principle | Atomic structure and properties | AP Chemistry | Khan Academy

TL;DR

Learn about electron configuration and the Aufbau principle, which explains the order in which electrons fill different subshells in an atom.

Transcript

• [Instructor] In other videos we introduced ourselves to the idea of orbitals and these are various orbitals in their various subshells that you could find in various shells of an atom. And in this video we're gonna get a little bit more practice with electron configuration. In particular, we're going to expose ourselves to the idea of the Aufbau ... Read More

Key Insights

• 🫀 Electron configuration describes how electrons occupy subshells in an atom.
• 😘 The Aufbau principle guides the filling of subshells, starting with the lowest energy levels and following an order based on increasing energy.
• 🫀 The electron configuration of an atom determines its chemical properties and behavior.
• 🤘 Transition metals, like scandium, have electron configurations that deviate from the expected pattern due to the Aufbau principle.

Questions & Answers

Q: What is electron configuration?

Electron configuration refers to how electrons are distributed among various subshells in an atom, following specific rules and principles.

Q: What is the Aufbau principle?

The Aufbau principle states that electrons fill lower energy subshells before moving on to higher energy ones, following an order based on increasing energy levels.

Q: How does electron configuration change as you move from neon to argon?

Neon's electron configuration is 1s2 2s2 2p6. In argon, two more electrons are added to fill the 3s subshell (3s2) and the 3p subshell (3p6).

Q: How does calcium's electron configuration differ from argon's?

Calcium's electron configuration is the same as argon's for the first 18 electrons (1s2 2s2 2p6 3s2 3p6). However, instead of filling the 3d subshell, the extra two electrons go into the 4s subshell (4s2).

Q: What is the electron configuration of scandium?

Scandium's electron configuration builds off of argon (1s2 2s2 2p6 3s2 3p6), with two electrons in the 4s subshell (4s2). The remaining electron goes into the 3d subshell (3d1).

Q: Why is the Aufbau principle sometimes taught with a different order for filling subshells in scandium?

While it is commonly taught to fill the 4s subshell before the 3d subshell in scandium, the actual addition of electrons to an atom starts with the 3d subshell, even though it appears first in the electron configuration.

Q: How does the Aufbau principle help with understanding electron configuration?

The Aufbau principle provides a systematic approach to determining the order in which subshells are filled with electrons, allowing for the prediction and understanding of electron configurations in various atoms.

Q: How are the elements categorized based on their electron configuration?

Elements that fill the S subshell are placed in the S block, whereas those that fill the P subshell are in the P block. The elements in the middle, including scandium, form the D block.

Summary & Key Takeaways

• Electron configuration describes how electrons occupy various subshells in an atom.

• The Aufbau principle guides the filling of subshells, starting from the lowest energy level.

• The electron configuration of an atom can be determined by following the order of subshells and filling them with the appropriate number of electrons.