What is Electron Configuration?
Electron configuration describes how electrons are distributed among an atom's orbitals. It determines an element's chemical properties, reactivity, and bonding behavior. For example, carbon's configuration is $1s^2\, 2s^2\, 2p^2$, meaning it has 2 electrons in the 1s orbital, 2 in 2s, and 2 in 2p.
How to Calculate Electron Configuration
Follow these steps to determine the electron configuration of any element:
The atomic number (Z) tells you how many electrons are in a neutral atom. For example, iron has Z = 26, so it has 26 electrons.
Electrons fill orbitals from lowest to highest energy. Use the diagram below to remember the order:
Follow the diagonal arrows from top-right to bottom-left
The filling sequence is: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p
Each subshell has a maximum capacity:
| Subshell | Number of Orbitals | Maximum Electrons |
|---|---|---|
| s | 1 | 2 |
| p | 3 | 6 |
| d | 5 | 10 |
| f | 7 | 14 |
Write each subshell with its electron count as a superscript. For example, oxygen (Z = 8) has the configuration $1s^2\, 2s^2\, 2p^4$.
Manual calculation works for simple elements, but it gets complex for transition metals and ions. Use our calculator above to get instant, accurate results for any element or ion—including all exceptions!
Detailed Examples
Example 1: Carbon (Z = 6)
Carbon has 6 electrons. Following the steps:
- Atomic number: Z = 6, so 6 electrons
- Fill in order: 1s (2 electrons) → 2s (2 electrons) → 2p (2 electrons)
- Write configuration: $1s^2\, 2s^2\, 2p^2$
Example 2: Iron (Z = 26)
Iron has 26 electrons:
- Fill orbitals: 1s² (2) → 2s² (4) → 2p⁶ (10) → 3s² (12) → 3p⁶ (18) → 4s² (20) → 3d⁶ (26)
- Full configuration: $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^6$
- Noble gas notation: $[\text{Ar}]\, 4s^2\, 3d^6$
How This Electron Configuration Calculator Works
The calculator automates the entire process:
- Select any element from the dropdown menu or click on the interactive periodic table
- Choose the charge for neutral atoms or ions (cations and anions from -5 to +5)
- Get instant results including full electron configuration, noble gas notation, shell distribution, and magnetic properties
- Automatic exception handling for elements like chromium, copper, molybdenum, silver, gold, and palladium
Perfect for students checking homework, teachers preparing lessons, or chemists needing quick reference data.
Noble Gas Notation: The Shortcut Method
Noble gas notation uses the symbol of the previous noble gas in square brackets to represent core electrons. This abbreviated form highlights only the valence electrons involved in chemical bonding.
Example: Iron (Fe)
Full configuration: $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^6$
Previous noble gas: Argon (Ar) has configuration $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6$
Noble gas notation: $[\text{Ar}]\, 4s^2\, 3d^6$
Example: Gold (Au)
Full configuration: $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^{10}\, 4p^6\, 5s^2\, 4f^{14}\, 5d^{10}\, 6s^1$
Previous noble gas: Xenon (Xe)
Noble gas notation: $[\text{Xe}]\, 6s^1\, 4f^{14}\, 5d^{10}$
Electron Configuration of Ions (Cations and Anions)
When atoms gain or lose electrons to form ions, their electron configurations change. The key rule: for transition metals, remove 4s electrons before 3d electrons when forming cations.
Students often remove electrons from 3d before 4s when forming cations. This is incorrect! Even though 4s fills first, it has higher energy once 3d starts filling, so 4s electrons are removed first.
Example 1: Iron(II) Ion (Fe²⁺)
Neutral Fe: $[\text{Ar}]\, 4s^2\, 3d^6$
Remove 2 electrons: Remove from 4s first (not 3d!)
Fe²⁺ configuration: $[\text{Ar}]\, 3d^6$
Example 2: Chloride Ion (Cl⁻)
Neutral Cl: $[\text{Ne}]\, 3s^2\, 3p^5$
Add 1 electron: Add to 3p orbital
Cl⁻ configuration: $[\text{Ne}]\, 3s^2\, 3p^6$ (same as Argon)
Exceptions to the Aufbau Principle
Several elements have electron configurations that deviate from the predicted Aufbau order. These exceptions occur because half-filled ($d^5$, $f^7$) and fully-filled ($d^{10}$, $f^{14}$) subshells have extra stability due to exchange energy and symmetrical electron distribution.
| Element | Z | Expected Configuration | Actual Configuration |
|---|---|---|---|
| Chromium | 24 | $[\text{Ar}]\, 4s^2\, 3d^4$ | $[\text{Ar}]\, 4s^1\, 3d^5$ |
| Copper | 29 | $[\text{Ar}]\, 4s^2\, 3d^9$ | $[\text{Ar}]\, 4s^1\, 3d^{10}$ |
| Molybdenum | 42 | $[\text{Kr}]\, 5s^2\, 4d^4$ | $[\text{Kr}]\, 5s^1\, 4d^5$ |
| Silver | 47 | $[\text{Kr}]\, 5s^2\, 4d^9$ | $[\text{Kr}]\, 5s^1\, 4d^{10}$ |
| Gold | 79 | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^9$ | $[\text{Xe}]\, 6s^1\, 4f^{14}\, 5d^{10}$ |
| Palladium | 46 | $[\text{Kr}]\, 5s^2\, 4d^8$ | $[\text{Kr}]\, 4d^{10}$ |
Why Chromium is $4s^1\, 3d^5$ Instead of $4s^2\, 3d^4$
Chromium promotes one 4s electron to 3d to achieve a half-filled 3d subshell ($3d^5$). This configuration has maximum exchange energy and symmetrical electron distribution, making it more stable than the expected $4s^2\, 3d^4$ configuration.
How Electron Configuration Relates to the Periodic Table
The periodic table is organized according to electron configuration. Each block corresponds to the subshell being filled with electrons.
| Block | Subshell Being Filled | Groups | Elements |
|---|---|---|---|
| s-block | ns | 1-2 (and He) | Alkali metals, alkaline earth metals, H, He |
| p-block | np | 13-18 | Boron group through noble gases |
| d-block | (n-1)d | 3-12 | Transition metals |
| f-block | (n-2)f | — | Lanthanides and actinides |
Elements in the same group have similar valence electron configurations, which explains why they have similar chemical properties. For example, all Group 1 elements (alkali metals) have one valence electron in an s orbital.
Understanding Shells: K, L, M, N
Electrons are organized into shells labeled K, L, M, N, O, P, and Q, corresponding to principal quantum numbers $n = 1, 2, 3, 4, 5, 6, 7$. Each shell can hold a maximum of $2n^2$ electrons.
| Shell | Principal Quantum Number (n) | Maximum Electrons ($2n^2$) |
|---|---|---|
| K | 1 | 2 |
| L | 2 | 8 |
| M | 3 | 18 |
| N | 4 | 32 |
| O | 5 | 50 |
| P | 6 | 72 |
| Q | 7 | 98 |
Shell Distribution for Iron (Fe)
Configuration: $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^6$
Group by shell:
- K shell (n=1): 1s² = 2 electrons
- L shell (n=2): 2s² + 2p⁶ = 8 electrons
- M shell (n=3): 3s² + 3p⁶ + 3d⁶ = 14 electrons
- N shell (n=4): 4s² = 2 electrons
Shell distribution: K=2, L=8, M=14, N=2
Paramagnetic vs Diamagnetic Elements
The magnetic properties of an element depend on whether it has unpaired electrons. You can determine this directly from the electron configuration using Hund's Rule.
| Property | Unpaired Electrons | Behavior in Magnetic Field | Examples |
|---|---|---|---|
| Paramagnetic | One or more | Attracted to magnetic field | Fe, O, Cu²⁺, Mn²⁺ |
| Diamagnetic | Zero (all paired) | Weakly repelled by magnetic field | Zn, Ne, Na⁺, Cl⁻ |
Example: Iron (Fe) is Paramagnetic
Configuration: $[\text{Ar}]\, 4s^2\, 3d^6$
The 3d subshell has 5 orbitals and 6 electrons. By Hund's Rule, 4 electrons occupy separate orbitals with parallel spins, and 1 orbital has a pair. This leaves 4 unpaired electrons, making iron strongly paramagnetic.
Example: Zinc (Zn) is Diamagnetic
Configuration: $[\text{Ar}]\, 4s^2\, 3d^{10}$
Both the 4s and 3d subshells are completely filled, meaning all electrons are paired. Zinc has zero unpaired electrons and is diamagnetic.
Complete Electron Configuration Table
Below is a complete table of electron configurations for all 118 known elements. Use the calculator above to explore ions and get additional properties like shell distribution and magnetic behavior.
| Z | Symbol | Name | Full Configuration | Noble Gas Notation |
|---|---|---|---|---|
| 1 | H | Hydrogen | $1s^1$ | $1s^1$ |
| 2 | He | Helium | $1s^2$ | $1s^2$ |
| 3 | Li | Lithium | $1s^2\, 2s^1$ | $[\text{He}]\, 2s^1$ |
| 4 | Be | Beryllium | $1s^2\, 2s^2$ | $[\text{He}]\, 2s^2$ |
| 5 | B | Boron | $1s^2\, 2s^2\, 2p^1$ | $[\text{He}]\, 2s^2\, 2p^1$ |
| 6 | C | Carbon | $1s^2\, 2s^2\, 2p^2$ | $[\text{He}]\, 2s^2\, 2p^2$ |
| 7 | N | Nitrogen | $1s^2\, 2s^2\, 2p^3$ | $[\text{He}]\, 2s^2\, 2p^3$ |
| 8 | O | Oxygen | $1s^2\, 2s^2\, 2p^4$ | $[\text{He}]\, 2s^2\, 2p^4$ |
| 9 | F | Fluorine | $1s^2\, 2s^2\, 2p^5$ | $[\text{He}]\, 2s^2\, 2p^5$ |
| 10 | Ne | Neon | $1s^2\, 2s^2\, 2p^6$ | $[\text{He}]\, 2s^2\, 2p^6$ |
| 11 | Na | Sodium | $1s^2\, 2s^2\, 2p^6\, 3s^1$ | $[\text{Ne}]\, 3s^1$ |
| 12 | Mg | Magnesium | $1s^2\, 2s^2\, 2p^6\, 3s^2$ | $[\text{Ne}]\, 3s^2$ |
| 13 | Al | Aluminum | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^1$ | $[\text{Ne}]\, 3s^2\, 3p^1$ |
| 14 | Si | Silicon | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^2$ | $[\text{Ne}]\, 3s^2\, 3p^2$ |
| 15 | P | Phosphorus | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^3$ | $[\text{Ne}]\, 3s^2\, 3p^3$ |
| 16 | S | Sulfur | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^4$ | $[\text{Ne}]\, 3s^2\, 3p^4$ |
| 17 | Cl | Chlorine | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^5$ | $[\text{Ne}]\, 3s^2\, 3p^5$ |
| 18 | Ar | Argon | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6$ | $[\text{Ne}]\, 3s^2\, 3p^6$ |
| 19 | K | Potassium | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^1$ | $[\text{Ar}]\, 4s^1$ |
| 20 | Ca | Calcium | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2$ | $[\text{Ar}]\, 4s^2$ |
| 21 | Sc | Scandium | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^1$ | $[\text{Ar}]\, 4s^2\, 3d^1$ |
| 22 | Ti | Titanium | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^2$ | $[\text{Ar}]\, 4s^2\, 3d^2$ |
| 23 | V | Vanadium | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^3$ | $[\text{Ar}]\, 4s^2\, 3d^3$ |
| 24 | Cr | Chromium | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^1\, 3d^5$ | $[\text{Ar}]\, 4s^1\, 3d^5$ |
| 25 | Mn | Manganese | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^5$ | $[\text{Ar}]\, 4s^2\, 3d^5$ |
| 26 | Fe | Iron | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^6$ | $[\text{Ar}]\, 4s^2\, 3d^6$ |
| 27 | Co | Cobalt | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^7$ | $[\text{Ar}]\, 4s^2\, 3d^7$ |
| 28 | Ni | Nickel | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^8$ | $[\text{Ar}]\, 4s^2\, 3d^8$ |
| 29 | Cu | Copper | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^1\, 3d^{10}$ | $[\text{Ar}]\, 4s^1\, 3d^{10}$ |
| 30 | Zn | Zinc | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^{10}$ | $[\text{Ar}]\, 4s^2\, 3d^{10}$ |
| 31 | Ga | Gallium | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^{10}\, 4p^1$ | $[\text{Ar}]\, 4s^2\, 3d^{10}\, 4p^1$ |
| 32 | Ge | Germanium | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^{10}\, 4p^2$ | $[\text{Ar}]\, 4s^2\, 3d^{10}\, 4p^2$ |
| 33 | As | Arsenic | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^{10}\, 4p^3$ | $[\text{Ar}]\, 4s^2\, 3d^{10}\, 4p^3$ |
| 34 | Se | Selenium | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^{10}\, 4p^4$ | $[\text{Ar}]\, 4s^2\, 3d^{10}\, 4p^4$ |
| 35 | Br | Bromine | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^{10}\, 4p^5$ | $[\text{Ar}]\, 4s^2\, 3d^{10}\, 4p^5$ |
| 36 | Kr | Krypton | $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^{10}\, 4p^6$ | $[\text{Ar}]\, 4s^2\, 3d^{10}\, 4p^6$ |
| 37 | Rb | Rubidium | $[\text{Kr}]\, 5s^1$ | $[\text{Kr}]\, 5s^1$ |
| 38 | Sr | Strontium | $[\text{Kr}]\, 5s^2$ | $[\text{Kr}]\, 5s^2$ |
| 39 | Y | Yttrium | $[\text{Kr}]\, 5s^2\, 4d^1$ | $[\text{Kr}]\, 5s^2\, 4d^1$ |
| 40 | Zr | Zirconium | $[\text{Kr}]\, 5s^2\, 4d^2$ | $[\text{Kr}]\, 5s^2\, 4d^2$ |
| 41 | Nb | Niobium | $[\text{Kr}]\, 5s^1\, 4d^4$ | $[\text{Kr}]\, 5s^1\, 4d^4$ |
| 42 | Mo | Molybdenum | $[\text{Kr}]\, 5s^1\, 4d^5$ | $[\text{Kr}]\, 5s^1\, 4d^5$ |
| 43 | Tc | Technetium | $[\text{Kr}]\, 5s^2\, 4d^5$ | $[\text{Kr}]\, 5s^2\, 4d^5$ |
| 44 | Ru | Ruthenium | $[\text{Kr}]\, 5s^1\, 4d^7$ | $[\text{Kr}]\, 5s^1\, 4d^7$ |
| 45 | Rh | Rhodium | $[\text{Kr}]\, 5s^1\, 4d^8$ | $[\text{Kr}]\, 5s^1\, 4d^8$ |
| 46 | Pd | Palladium | $[\text{Kr}]\, 4d^{10}$ | $[\text{Kr}]\, 4d^{10}$ |
| 47 | Ag | Silver | $[\text{Kr}]\, 5s^1\, 4d^{10}$ | $[\text{Kr}]\, 5s^1\, 4d^{10}$ |
| 48 | Cd | Cadmium | $[\text{Kr}]\, 5s^2\, 4d^{10}$ | $[\text{Kr}]\, 5s^2\, 4d^{10}$ |
| 49 | In | Indium | $[\text{Kr}]\, 5s^2\, 4d^{10}\, 5p^1$ | $[\text{Kr}]\, 5s^2\, 4d^{10}\, 5p^1$ |
| 50 | Sn | Tin | $[\text{Kr}]\, 5s^2\, 4d^{10}\, 5p^2$ | $[\text{Kr}]\, 5s^2\, 4d^{10}\, 5p^2$ |
| 51 | Sb | Antimony | $[\text{Kr}]\, 5s^2\, 4d^{10}\, 5p^3$ | $[\text{Kr}]\, 5s^2\, 4d^{10}\, 5p^3$ |
| 52 | Te | Tellurium | $[\text{Kr}]\, 5s^2\, 4d^{10}\, 5p^4$ | $[\text{Kr}]\, 5s^2\, 4d^{10}\, 5p^4$ |
| 53 | I | Iodine | $[\text{Kr}]\, 5s^2\, 4d^{10}\, 5p^5$ | $[\text{Kr}]\, 5s^2\, 4d^{10}\, 5p^5$ |
| 54 | Xe | Xenon | $[\text{Kr}]\, 5s^2\, 4d^{10}\, 5p^6$ | $[\text{Kr}]\, 5s^2\, 4d^{10}\, 5p^6$ |
| 55 | Cs | Cesium | $[\text{Xe}]\, 6s^1$ | $[\text{Xe}]\, 6s^1$ |
| 56 | Ba | Barium | $[\text{Xe}]\, 6s^2$ | $[\text{Xe}]\, 6s^2$ |
| 57 | La | Lanthanum | $[\text{Xe}]\, 6s^2\, 5d^1$ | $[\text{Xe}]\, 6s^2\, 5d^1$ |
| 58 | Ce | Cerium | $[\text{Xe}]\, 6s^2\, 4f^1\, 5d^1$ | $[\text{Xe}]\, 6s^2\, 4f^1\, 5d^1$ |
| 59 | Pr | Praseodymium | $[\text{Xe}]\, 6s^2\, 4f^3$ | $[\text{Xe}]\, 6s^2\, 4f^3$ |
| 60 | Nd | Neodymium | $[\text{Xe}]\, 6s^2\, 4f^4$ | $[\text{Xe}]\, 6s^2\, 4f^4$ |
| 61 | Pm | Promethium | $[\text{Xe}]\, 6s^2\, 4f^5$ | $[\text{Xe}]\, 6s^2\, 4f^5$ |
| 62 | Sm | Samarium | $[\text{Xe}]\, 6s^2\, 4f^6$ | $[\text{Xe}]\, 6s^2\, 4f^6$ |
| 63 | Eu | Europium | $[\text{Xe}]\, 6s^2\, 4f^7$ | $[\text{Xe}]\, 6s^2\, 4f^7$ |
| 64 | Gd | Gadolinium | $[\text{Xe}]\, 6s^2\, 4f^7\, 5d^1$ | $[\text{Xe}]\, 6s^2\, 4f^7\, 5d^1$ |
| 65 | Tb | Terbium | $[\text{Xe}]\, 6s^2\, 4f^9$ | $[\text{Xe}]\, 6s^2\, 4f^9$ |
| 66 | Dy | Dysprosium | $[\text{Xe}]\, 6s^2\, 4f^{10}$ | $[\text{Xe}]\, 6s^2\, 4f^{10}$ |
| 67 | Ho | Holmium | $[\text{Xe}]\, 6s^2\, 4f^{11}$ | $[\text{Xe}]\, 6s^2\, 4f^{11}$ |
| 68 | Er | Erbium | $[\text{Xe}]\, 6s^2\, 4f^{12}$ | $[\text{Xe}]\, 6s^2\, 4f^{12}$ |
| 69 | Tm | Thulium | $[\text{Xe}]\, 6s^2\, 4f^{13}$ | $[\text{Xe}]\, 6s^2\, 4f^{13}$ |
| 70 | Yb | Ytterbium | $[\text{Xe}]\, 6s^2\, 4f^{14}$ | $[\text{Xe}]\, 6s^2\, 4f^{14}$ |
| 71 | Lu | Lutetium | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^1$ | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^1$ |
| 72 | Hf | Hafnium | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^2$ | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^2$ |
| 73 | Ta | Tantalum | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^3$ | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^3$ |
| 74 | W | Tungsten | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^4$ | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^4$ |
| 75 | Re | Rhenium | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^5$ | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^5$ |
| 76 | Os | Osmium | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^6$ | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^6$ |
| 77 | Ir | Iridium | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^7$ | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^7$ |
| 78 | Pt | Platinum | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^8$ | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^8$ |
| 79 | Au | Gold | $[\text{Xe}]\, 6s^1\, 4f^{14}\, 5d^{10}$ | $[\text{Xe}]\, 6s^1\, 4f^{14}\, 5d^{10}$ |
| 80 | Hg | Mercury | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^{10}$ | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^{10}$ |
| 81 | Tl | Thallium | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^{10}\, 6p^1$ | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^{10}\, 6p^1$ |
| 82 | Pb | Lead | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^{10}\, 6p^2$ | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^{10}\, 6p^2$ |
| 83 | Bi | Bismuth | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^{10}\, 6p^3$ | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^{10}\, 6p^3$ |
| 84 | Po | Polonium | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^{10}\, 6p^4$ | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^{10}\, 6p^4$ |
| 85 | At | Astatine | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^{10}\, 6p^5$ | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^{10}\, 6p^5$ |
| 86 | Rn | Radon | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^{10}\, 6p^6$ | $[\text{Xe}]\, 6s^2\, 4f^{14}\, 5d^{10}\, 6p^6$ |
| 87 | Fr | Francium | $[\text{Rn}]\, 7s^1$ | $[\text{Rn}]\, 7s^1$ |
| 88 | Ra | Radium | $[\text{Rn}]\, 7s^2$ | $[\text{Rn}]\, 7s^2$ |
| 89 | Ac | Actinium | $[\text{Rn}]\, 7s^2\, 6d^1$ | $[\text{Rn}]\, 7s^2\, 6d^1$ |
| 90 | Th | Thorium | $[\text{Rn}]\, 7s^2\, 6d^2$ | $[\text{Rn}]\, 7s^2\, 6d^2$ |
| 91 | Pa | Protactinium | $[\text{Rn}]\, 7s^2\, 5f^2\, 6d^1$ | $[\text{Rn}]\, 7s^2\, 5f^2\, 6d^1$ |
| 92 | U | Uranium | $[\text{Rn}]\, 7s^2\, 5f^3\, 6d^1$ | $[\text{Rn}]\, 7s^2\, 5f^3\, 6d^1$ |
| 93 | Np | Neptunium | $[\text{Rn}]\, 7s^2\, 5f^4\, 6d^1$ | $[\text{Rn}]\, 7s^2\, 5f^4\, 6d^1$ |
| 94 | Pu | Plutonium | $[\text{Rn}]\, 7s^2\, 5f^6$ | $[\text{Rn}]\, 7s^2\, 5f^6$ |
| 95 | Am | Americium | $[\text{Rn}]\, 7s^2\, 5f^7$ | $[\text{Rn}]\, 7s^2\, 5f^7$ |
| 96 | Cm | Curium | $[\text{Rn}]\, 7s^2\, 5f^7\, 6d^1$ | $[\text{Rn}]\, 7s^2\, 5f^7\, 6d^1$ |
| 97 | Bk | Berkelium | $[\text{Rn}]\, 7s^2\, 5f^9$ | $[\text{Rn}]\, 7s^2\, 5f^9$ |
| 98 | Cf | Californium | $[\text{Rn}]\, 7s^2\, 5f^{10}$ | $[\text{Rn}]\, 7s^2\, 5f^{10}$ |
| 99 | Es | Einsteinium | $[\text{Rn}]\, 7s^2\, 5f^{11}$ | $[\text{Rn}]\, 7s^2\, 5f^{11}$ |
| 100 | Fm | Fermium | $[\text{Rn}]\, 7s^2\, 5f^{12}$ | $[\text{Rn}]\, 7s^2\, 5f^{12}$ |
| 101 | Md | Mendelevium | $[\text{Rn}]\, 7s^2\, 5f^{13}$ | $[\text{Rn}]\, 7s^2\, 5f^{13}$ |
| 102 | No | Nobelium | $[\text{Rn}]\, 7s^2\, 5f^{14}$ | $[\text{Rn}]\, 7s^2\, 5f^{14}$ |
| 103 | Lr | Lawrencium | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 7p^1$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 7p^1$ |
| 104 | Rf | Rutherfordium | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^2$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^2$ |
| 105 | Db | Dubnium | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^3$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^3$ |
| 106 | Sg | Seaborgium | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^4$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^4$ |
| 107 | Bh | Bohrium | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^5$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^5$ |
| 108 | Hs | Hassium | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^6$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^6$ |
| 109 | Mt | Meitnerium | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^7$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^7$ |
| 110 | Ds | Darmstadtium | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^8$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^8$ |
| 111 | Rg | Roentgenium | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^9$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^9$ |
| 112 | Cn | Copernicium | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^{10}$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^{10}$ |
| 113 | Nh | Nihonium | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^{10}\, 7p^1$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^{10}\, 7p^1$ |
| 114 | Fl | Flerovium | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^{10}\, 7p^2$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^{10}\, 7p^2$ |
| 115 | Mc | Moscovium | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^{10}\, 7p^3$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^{10}\, 7p^3$ |
| 116 | Lv | Livermorium | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^{10}\, 7p^4$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^{10}\, 7p^4$ |
| 117 | Ts | Tennessine | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^{10}\, 7p^5$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^{10}\, 7p^5$ |
| 118 | Og | Oganesson | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^{10}\, 7p^6$ | $[\text{Rn}]\, 7s^2\, 5f^{14}\, 6d^{10}\, 7p^6$ |
Frequently Asked Questions
How do you find the electron configuration of an element?
Find the element's atomic number, which equals the number of electrons in a neutral atom. Then fill orbitals in Aufbau order (1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, etc.) until all electrons are placed, respecting each subshell's capacity (s=2, p=6, d=10, f=14). The calculator above automates this process for all 118 elements.
Why does chromium have 4s¹ 3d⁵ instead of 4s² 3d⁴?
Chromium is an exception to the Aufbau Principle because a half-filled 3d subshell ($3d^5$) has extra stability due to exchange energy and symmetrical electron distribution. The energy gained from this stability outweighs the energy cost of promoting one electron from 4s to 3d. Similar exceptions occur for copper, molybdenum, silver, and gold.
How do you write electron configuration for ions?
For cations (positive ions), remove electrons from the neutral atom's configuration, starting with the highest principal quantum number $n$ first. For transition metals, this means removing 4s electrons before 3d electrons. For anions (negative ions), add electrons to the next available orbital following the Aufbau order. The calculator above handles both cations and anions automatically.
What is noble gas notation?
Noble gas notation (also called condensed or abbreviated electron configuration) uses the symbol of the previous noble gas in square brackets to represent the core electrons. For example, iron's full configuration is $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^2\, 3d^6$, but in noble gas notation it is written as $[\text{Ar}]\, 4s^2\, 3d^6$. This notation is shorter and highlights only the valence electrons involved in bonding.
What are valence electrons?
Valence electrons are the electrons in the outermost shell (highest principal quantum number $n$) of an atom. These electrons are involved in chemical bonding and determine an element's chemical properties. For main group elements, the number of valence electrons equals the group number (for Groups 1-2) or the group number minus 10 (for Groups 13-18).
What makes an element paramagnetic vs diamagnetic?
An element is paramagnetic if it has one or more unpaired electrons, causing it to be attracted to a magnetic field. An element is diamagnetic if all its electrons are paired, causing it to be weakly repelled by a magnetic field. You can determine this from the electron configuration using Hund's Rule: if any subshell has unpaired electrons, the element is paramagnetic.
Why are 4s electrons removed before 3d in cations?
Although 4s fills before 3d when building up the atom (because 4s has lower energy when empty), once 3d starts filling, the 3d electrons actually have lower energy than 4s. When forming cations, electrons are removed from the highest energy level first, which is 4s. This is why Fe²⁺ is $[\text{Ar}]\, 3d^6$, not $[\text{Ar}]\, 4s^2\, 3d^4$.
How many electrons can each orbital hold?
Each individual orbital can hold a maximum of 2 electrons with opposite spins (Pauli Exclusion Principle). Each subshell contains a specific number of orbitals: s has 1 orbital (holds 2 electrons), p has 3 orbitals (holds 6 electrons), d has 5 orbitals (holds 10 electrons), and f has 7 orbitals (holds 14 electrons).
References
The formulas, examples, and data presented in this calculator are based on established principles of quantum chemistry from the following sources: