Electron Configuration Calculator
Find electron configurations for all elements in the periodic table
View atomic number, atomic mass, and valence electrons for any element
Understanding Electron Configuration
Electron configuration describes how electrons are arranged in the orbitals and shells of an atom. Think of it as an address system where each electron has a unique location in the atom. This arrangement is not random—it follows fundamental rules of quantum mechanics and directly determines the chemical and physical properties of an element.
Why does this matter?
The way electrons are distributed explains why atoms react the way they do, what colors they display, and how strong their bonds are.
Orbitals & Shells
Orbitals are 3D regions where electrons are likely to be found. They are organized into shells (energy levels) and subshells (s, p, d, f).
Core Principles & Rules
Aufbau Principle
Electrons occupy the lowest energy orbitals first (1s before 2s).
Pauli Exclusion
An orbital can hold max 2 electrons with opposite spins.
Hund's Rule
Electrons fill empty orbitals singly before pairing up.
The Filling Sequence (Aufbau Order)
Energy Level Exception
Notice that 4s fills before 3d. While the 4th shell is technically "outside" the 3rd, the 4s orbital actually has a lower energy level than 3d, making it easier for electrons to occupy first.
What are Valence Electrons?
Valence electrons are the electrons in the outermost shell of an atom. These are the most important electrons because they determine how an element reacts and bonds with others.
Group 1
ns¹
1 e⁻
Group 14
ns² np²
4 e⁻
Group 17
ns² np⁵
7 e⁻
Group 18
ns² np⁶
8 e⁻
Chemistry in the Real World
Why is Sodium (Na) so Reactive?
Sodium has the configuration 1s² 2s² 2p⁶ 3s¹. That single electron in the 3s orbital is very unstable. If sodium loses it, it becomes a stable sodium ion (Na⁺) with a full outer shell like Neon. This "desire" to achieve stability is why sodium reacts violently with water.
Noble Gas Stability
Noble gases like Argon ([Ne] 3s² 3p⁶) have completely filled outer shells. Since they already have the maximum number of valence electrons, they don't need to react, making them the most stable elements in nature.
Frequently Asked Questions
Why do some elements have 'unusual' configurations?
Chromium and Copper are common exceptions. They move an electron from the 4s to the 3d orbital because half-filled (d⁵) or fully-filled (d¹⁰) subshells are extra stable.
How do I find configuration for ions?
For positive ions (cations), remove electrons starting from the highest energy level. For negative ions (anions), add electrons to the next available orbital.
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