Electron Configuration- How to Write It Using the Periodic Table

What Is Electron Configuration?

Electron configuration tells you how electrons are arranged in an atom. That's it. No fancy definitions needed.

Every element's chemical behavior comes down to where its electrons sit. If you can write electron configurations correctly, you understand why elements react the way they do. This isn't optional knowledge—it's the foundation of chemistry.

The Basics You Need First

Before touching the periodic table, you need to know these rules:

• Electrons fill orbitals in order of increasing energy
• Each orbital holds a maximum of 2 electrons
• s orbitals hold 2, p orbitals hold 6, d orbitals hold 10, f orbitals hold 14
• You follow the Aufbau principle—that's just "electrons fill lowest energy first"

The Orbital Energy Order

This sequence tells you the filling order. Memorize it or write it down:

1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p

Notice 4s fills before 3d. This trips up students constantly. Don't let it trip you up.

How the Periodic Table Gives You Electron Configurations

The periodic table isn't random. Its structure directly corresponds to electron filling. Once you see this, writing configurations becomes mechanical.

The Four Blocks

The periodic table splits into four blocks based on which subshell electrons enter:

• s-block: Groups 1 and 2 (plus He)
• p-block: Groups 13-18
• d-block: The transition metals (Groups 3-12)
• f-block: Lanthanides and actinides (the rows at the bottom)

Reading the Period and Group Numbers

Here's the pattern that makes everything click:

• The period number tells you the highest energy level (n)
• The group number in the s or p blocks tells you valence electrons
• The last orbital filled determines which block you're in

For d-block elements, the d subshell is always one energy level behind the period. For example, Period 4 d-block elements fill the 3d orbital.

Step-by-Step: Writing Electron Configurations

Let's do this properly with two examples.

Example 1: Nitrogen (N), Atomic Number 7

Nitrogen has 7 electrons. Follow the filling order:

1s² → 2s² → 2p³

That's the full configuration. Shorthand notation uses the previous noble gas:

[He] 2s² 2p³

Count your electrons: 2 + 2 + 3 = 7. Correct.

Example 2: Chlorine (Cl), Atomic Number 17

Follow the filling order with 17 electrons:

1s² 2s² 2p⁶ 3s² 3p⁵

Shorthand: [Ne] 3s² 3p⁵

Notice the superscripts add up to your total electrons. Always verify this.

Electron Configurations for All Elements (Key Examples)

The Exceptions Nobody Warns You About

Chromium (Cr) and Copper (Cu) are the famous problem children.

Chromium should be [Ar] 4s² 3d⁴, but it's actually [Ar] 4s¹ 3d⁵.

Copper should be [Ar] 4s² 3d⁹, but it's actually [Ar] 4s¹ 3d¹⁰.

Why? Half-filled and fully-filled d subshells have extra stability. Chemistry rewards electrons that find these configurations. Accept it and move on.

Orbital Diagrams: Visualizing Electron Spins

Sometimes you need more than the configuration. Orbital diagrams show individual electron placement with spin arrows.

Rules for orbital diagrams:

• Each orbital gets one electron before any gets two (Hund's rule)
• Paired electrons have opposite spins
• Use up and down arrows to show spin

For carbon (1s² 2s² 2p²), the 2p orbitals look like this:

2p: ↑_ ↑_ __

Three separate orbitals, each with one electron, all spinning the same direction. That's Hund's rule in action.

Quick Reference: The Filling Order in Plain Terms

Add these up: 2 + 8 + 18 + 32 = 60 electrons maximum for n=4. The math checks out.

Getting Started: Your Practice Routine

You learn this by doing, not reading. Here's your workout:

1. Write the full configuration for the first 20 elements from memory
2. Convert each to shorthand notation using the previous noble gas
3. Draw orbital diagrams for the valence electrons of elements 1-10
4. Identify why Cr and Cu have their specific exceptions
5. Practice the d-block elements: Period 4 transition metals

Do this three times. By the fourth attempt, it'll stick.

What Actually Matters

You don't need to memorize every configuration forever. You need to understand the system well enough to derive any configuration on the spot.

The periodic table does the heavy lifting. Learn its structure, know the filling order, and you can write any electron configuration in under a minute.

That's the entire skill. Stop overcomplicating it.