Lewis Structure Calculator

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Lewis Structure Electron Calculator

Calculate valence electrons, bonding pairs, and lone pairs for molecules.

Total Valence Electrons (N): 0
Octet Requirement (H=2, others=8): 0
Shared Electrons (S = Octet – N): 0
Number of Bonds (S / 2): 0
Lone Pair Electrons (N – S): 0
Number of Lone Pairs: 0

How to Calculate Lewis Structures

Drawing a Lewis structure is a fundamental skill in chemistry used to visualize the bonding between atoms and the lone pairs of electrons that may exist in a molecule. Follow these steps used by our calculator:

1. Count Total Valence Electrons

Find the number of valence electrons for each atom using the periodic table (e.g., Group 14 has 4, Group 16 has 6). Sum them up and adjust for the molecular charge. Subtract electrons for positive charges and add electrons for negative charges.

2. Calculate the Octet Requirement

To be stable, most atoms "want" 8 electrons in their outer shell (the Octet Rule). Hydrogen is an exception, requiring only 2 electrons. The total octet requirement is the sum of these target numbers for all atoms in the molecule.

3. Determine Shared Electrons (Bonds)

Subtract the total valence electrons from the octet requirement. This difference tells you how many electrons must be shared to satisfy everyone's needs. Divide this number by 2 to find the total number of chemical bonds.

4. Determine Lone Pairs

Subtract the shared electrons from the total valence electrons. The remaining electrons are non-bonding (lone pairs). Divide by 2 to get the specific number of lone pairs to draw around the atoms.

Example Calculation: Carbon Dioxide (CO₂)

  • Atoms: 1 Carbon (4e⁻), 2 Oxygen (6e⁻ each).
  • Total Valence: 4 + (2 × 6) = 16 electrons.
  • Octet Requirement: 8 (C) + (2 × 8 for O) = 24 electrons.
  • Shared Electrons: 24 – 16 = 8 electrons (4 bonds).
  • Lone Pair Electrons: 16 – 8 = 8 electrons (4 lone pairs).
function calculateLewis() { var v1 = parseFloat(document.getElementById('v1').value) || 0; var q1 = parseFloat(document.getElementById('q1').value) || 0; var v2 = parseFloat(document.getElementById('v2').value) || 0; var q2 = parseFloat(document.getElementById('q2').value) || 0; var v3 = parseFloat(document.getElementById('v3').value) || 0; var q3 = parseFloat(document.getElementById('q3').value) || 0; var charge = parseFloat(document.getElementById('netCharge').value) || 0; // Total Valence Electrons (N) // Subtract charge because a positive charge means fewer electrons var totalValence = (v1 * q1) + (v2 * q2) + (v3 * q3) – charge; // Octet Requirement // Simple logic: If valence is 1 (Hydrogen), requirement is 2. Otherwise 8. var octet1 = (v1 === 1) ? 2 : 8; var octet2 = (v2 === 1) ? 2 : 8; var octet3 = (v3 === 1) ? 2 : 8; // Handle cases where v is 0 (empty rows) if(v1 === 0) octet1 = 0; if(v2 === 0) octet2 = 0; if(v3 === 0) octet3 = 0; var totalOctet = (octet1 * q1) + (octet2 * q2) + (octet3 * q3); // Shared Electrons (S) var sharedElectrons = totalOctet – totalValence; if (sharedElectrons < 0) sharedElectrons = 0; var bonds = sharedElectrons / 2; // Lone Pair Electrons var lonePairElectrons = totalValence – sharedElectrons; if (lonePairElectrons < 0) lonePairElectrons = 0; var lonePairs = lonePairElectrons / 2; // Display results document.getElementById('res-total-v').innerHTML = totalValence; document.getElementById('res-octet').innerHTML = totalOctet; document.getElementById('res-shared').innerHTML = sharedElectrons; document.getElementById('res-bonds').innerHTML = bonds.toFixed(1); document.getElementById('res-lone-e').innerHTML = lonePairElectrons; document.getElementById('res-lone-p').innerHTML = lonePairs.toFixed(1); document.getElementById('lewis-results').style.display = 'block'; }

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