Ever wondered how electrons arrange themselves around an atom's nucleus?...
Chemistry215 views·Updated 23 Aug 2026·2 pagesUnderstanding Electron Configuration
1
of 2
The Basics of Electron Configuration
Think of atomic orbitals as parking spaces around the nucleus where electrons hang out. Each orbital can hold a maximum of two electrons, but they must have opposite spins - like two people sharing a seat facing different directions.
There are four main types of orbitals: s, p, d, and f orbitals. A subshell is basically all the orbitals of the same type within the same energy level. For example, the 3d subshell contains all the d orbitals in the third shell.
Here's the key rule: electrons always fill the lowest energy orbitals first. It's like water flowing downhill - electrons naturally go where they need the least energy. When orbitals have the same energy level, electrons prefer to spread out into separate orbitals before pairing up, since they repel each other.
Quick Tip: Remember that nitrogen's electron configuration (1s² 2s² 2p³) shows how the 2p electrons spread out individually before pairing up!
2
of 2
Energy Levels and Notable Exceptions
Here's where it gets interesting: the 4s subshell actually has lower energy than the 3d subshell, even though 4s is in a higher shell number. This means electrons fill 4s before 3d, but when we write electron configurations, we still list them in shell order.
Iron's configuration perfectly demonstrates this: Fe: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s². Notice how 4s fills before 3d, but we write 3d before 4s in the final configuration.
However, chromium and copper are rebels that break the normal rules. Chromium ends up as 3d⁵ 4s¹ instead of 3d⁴ 4s², whilst copper becomes 3d¹⁰ 4s¹ rather than 3d⁹ 4s². Why? Because 3d subshells are more stable when they're either half-full or completely full.
Memory Hook: Think of it like this - sometimes it's worth breaking the rules to achieve perfect balance, just like chromium and copper do for stability!
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Chemistry215 views·Updated 23 Aug 2026·2 pagesUnderstanding Electron Configuration
Ever wondered how electrons arrange themselves around an atom's nucleus? Understanding electron configuration is like learning the seating plan for electrons - they follow specific rules about where they can sit and in what order they fill up the available...
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of 2
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The Basics of Electron Configuration
Think of atomic orbitals as parking spaces around the nucleus where electrons hang out. Each orbital can hold a maximum of two electrons, but they must have opposite spins - like two people sharing a seat facing different directions.
There are four main types of orbitals: s, p, d, and f orbitals. A subshell is basically all the orbitals of the same type within the same energy level. For example, the 3d subshell contains all the d orbitals in the third shell.
Here's the key rule: electrons always fill the lowest energy orbitals first. It's like water flowing downhill - electrons naturally go where they need the least energy. When orbitals have the same energy level, electrons prefer to spread out into separate orbitals before pairing up, since they repel each other.
Quick Tip: Remember that nitrogen's electron configuration (1s² 2s² 2p³) shows how the 2p electrons spread out individually before pairing up!
2
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Energy Levels and Notable Exceptions
Here's where it gets interesting: the 4s subshell actually has lower energy than the 3d subshell, even though 4s is in a higher shell number. This means electrons fill 4s before 3d, but when we write electron configurations, we still list them in shell order.
Iron's configuration perfectly demonstrates this: Fe: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s². Notice how 4s fills before 3d, but we write 3d before 4s in the final configuration.
However, chromium and copper are rebels that break the normal rules. Chromium ends up as 3d⁵ 4s¹ instead of 3d⁴ 4s², whilst copper becomes 3d¹⁰ 4s¹ rather than 3d⁹ 4s². Why? Because 3d subshells are more stable when they're either half-full or completely full.
Memory Hook: Think of it like this - sometimes it's worth breaking the rules to achieve perfect balance, just like chromium and copper do for stability!
We thought you’d never ask...
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
You can download the app from Google Play Store and Apple App Store.
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