Subjects

AP Chemistry

Acids and Bases

•

Dec 2, 2025

•

2 pages

Atomic Structure Basics: Key Concepts in Unit 1.5

Emma

@emmarogers

Dive into the fascinating world of atomic structure, where we'll... Show more

Unit 1.5
# Atomic Structure
## 3 PRINCIPIES
Aufbau's Principle: states that the electrons fill lower energy atomic
Building up
orbitals befo

Atomic Structure Principles

Ever wondered how electrons organize themselves around an atom? Three key principles govern this microscopic dance. Aufbau's Principle tells us that electrons are like economy-minded shoppers - they always fill the lowest energy orbitals first to minimize total energy.

Hund's Rule reveals that electrons prefer to stay unpaired when possible. When orbitals of equal energy are available, electrons will occupy them singly before pairing up - they're like solo travelers who prefer their own space!

According to Pauli's Exclusion Principle, when two electrons must share the same orbital, they'll have opposite spins to reduce repulsion. Think of them as roommates who face opposite directions to maintain peace.

Pro Tip: Remember "AHP" $Aufbau-Hund-Pauli$ as the three principles that determine electron configuration. This order also reflects how you should approach electron filling problems.

Electrons organize into an electron cloud surrounding the nucleus, which is divided into energy levels or shells (up to seven possible). Each energy level contains sublevels (s, p, d, f), which are further divided into orbitals where electrons are likely found. The sublevel structure determines how many electrons can fit:

s sublevel: 1 orbital holding 2 electrons maximum
p sublevel: 3 orbitals holding 6 electrons maximum
d sublevel: 5 orbitals holding 10 electrons maximum
f sublevel: 7 orbitals holding 14 electrons maximum

Orbital Diagrams

Orbital diagrams are visual representations that show exactly how electrons are arranged within orbitals. They're like apartment floor plans for electrons, showing which rooms (orbitals) are occupied and by how many tenants.

The "s" box represents an s orbital, which can hold up to two electrons. When drawn in an orbital diagram, a single electron in an s orbital is shown as an up arrow (↑), indicating its spin.

The "p" box represents a p orbital, and when electrons are paired within any orbital, they're shown as up and down arrows (↑↓). This opposite-direction representation illustrates how paired electrons have opposite spins, following Pauli's Exclusion Principle.

Remember: When filling orbitals, always follow the order: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p, etc. This pattern follows the increasing energy levels of the orbitals.

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Subjects

AP Chemistry

Acids and Bases

AP Chemistry

•

Dec 2, 2025

•

2 pages

Atomic Structure Basics: Key Concepts in Unit 1.5

Emma

@emmarogers

Dive into the fascinating world of atomic structure, where we'll explore how electrons are arranged around the nucleus. Understanding these patterns is key to predicting chemical behavior and forms the foundation of modern chemistry.

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Atomic Structure Principles

Pro Tip: Remember "AHP" $Aufbau-Hund-Pauli$ as the three principles that determine electron configuration. This order also reflects how you should approach electron filling problems.

s sublevel: 1 orbital holding 2 electrons maximum
p sublevel: 3 orbitals holding 6 electrons maximum
d sublevel: 5 orbitals holding 10 electrons maximum
f sublevel: 7 orbitals holding 14 electrons maximum

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Orbital Diagrams

The "s" box represents an s orbital, which can hold up to two electrons. When drawn in an orbital diagram, a single electron in an s orbital is shown as an up arrow (↑), indicating its spin.

Remember: When filling orbitals, always follow the order: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p, etc. This pattern follows the increasing energy levels of the orbitals.