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What is electronic configuration?

Electronic configuration describes how electrons are distributed among the atomic orbitals of an element. This distribution follows the Aufbau principle, which states that electrons fill orbitals in order of increasing energy. The electron configuration determines an element’s chemical properties, reactivity, and behavior—especially its valence electrons, which participate in chemical bonding.

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The Aufbau principle

Electrons fill orbitals in a specific sequence based on energy levels. SemiCode Analyzer implements this using the following orbital sequence: 
const sequence = [
  { n: "1s", max: 2 }, { n: "2s", max: 2 }, { n: "2p", max: 6 },
  { n: "3s", max: 2 }, { n: "3p", max: 6 }, { n: "4s", max: 2 },
  { n: "3d", max: 10 }, { n: "4p", max: 6 }, { n: "5s", max: 2 },
  { n: "4d", max: 10 }, { n: "5p", max: 6 }, { n: "6s", max: 2 },
  { n: "4f", max: 14 }, { n: "5d", max: 10 }, { n: "6p", max: 6 },
  { n: "7s", max: 2 }, { n: "5f", max: 14 }, { n: "6d", max: 10 },
  { n: "7p", max: 6 }
];
Notice that the filling order doesn’t always follow numerical order. For example, 4s fills before 3d because it has lower energy.

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Orbital capacity

Each type of orbital can hold a maximum number of electrons:
Orbital TypeMaximum Electrons
s2
p6
d10
f14
These limits reflect the quantum mechanical properties of atomic orbitals and Pauli’s exclusion principle.

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Valence electrons

Valence electrons are the electrons in the outermost energy level (highest principal quantum number). These electrons determine an element’s chemical behavior and bonding characteristics. SemiCode Analyzer calculates valence electrons by tracking the highest energy level: 
let currentLevel = parseInt(sub.n[0]);
if (currentLevel > lastLevel) {
  lastLevel = currentLevel;
  valenceElectrons = count;
} else if (currentLevel === lastLevel) {
  valenceElectrons += count;
}

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Example: Silicon (Z=14)

Silicon has 14 electrons distributed as:
  • 1s² 2s² 2p⁶ 3s² 3p²
  • The highest energy level is n=3 with 4 electrons (2 in 3s, 2 in 3p)
  • Therefore, Silicon has 4 valence electrons
Elements with 4 valence electrons like Silicon and Germanium are ideal semiconductors because they form stable covalent bonds but can be easily modified through doping.

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Examples

Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p²Valence electrons: 4 (in level 3)Significance: Pure semiconductor with complete tetrahedral bonding structure

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Energy level distribution

Beyond valence electrons, you can examine the complete distribution across all energy levels using getElectronsPerLevel(z): 
// For Silicon (Z=14)
const levels = getElectronsPerLevel(14);
// Returns: { 1: 2, 2: 8, 3: 4, 4: 0, 5: 0, 6: 0, 7: 0 }
This shows:
  • Level 1: 2 electrons (1s²)
  • Level 2: 8 electrons (2s² 2p⁶)
  • Level 3: 4 electrons (3s² 3p²)
  • Levels 4-7: empty

Semiconductor types

Learn how valence electrons determine semiconductor classification

Doping

Discover how adding elements with different valence counts modifies properties

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