Calculate Formal Charge

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Formal Charge Calculator

Number of valence electrons in the neutral free atom.
Total number of electrons in lone pairs (count each electron individually).
Total number of electrons shared in bonds (2 per single bond, 4 per double, 6 per triple).

Formal Charge (FC) = 0

What is Formal Charge?

In chemistry, the formal charge is the charge assigned to an atom in a molecule, assuming that electrons in all chemical bonds are shared equally between atoms, regardless of relative electronegativity. It is a theoretical tool used by chemists to determine the most likely Lewis structure for a molecule.

The Formal Charge Formula

FC = [V] – [N] – [B / 2]

  • V: Number of valence electrons in the neutral atom in its ground state.
  • N: Number of non-bonding valence electrons on the atom in the molecule (lone pair electrons).
  • B: Total number of electrons shared in bonds with other atoms.

Practical Example: Carbon Monoxide (CO)

Let's calculate the formal charge of Carbon in Carbon Monoxide (:C≡O:).

  1. Valence Electrons (V): Carbon is in Group 14, so V = 4.
  2. Non-bonding Electrons (N): Carbon has 1 lone pair, so N = 2.
  3. Bonding Electrons (B): There is a triple bond, so B = 6.
  4. Calculation: FC = 4 – 2 – (6 / 2) = 4 – 2 – 3 = -1.

In this specific Lewis structure, Carbon carries a formal charge of -1 and Oxygen carries a formal charge of +1.

Why Does Formal Charge Matter?

Determining formal charges helps in predicting the stability of resonance structures. Generally, the most stable structure is the one where:

  1. Formal charges are closest to zero.
  2. Negative formal charges reside on the most electronegative atoms.
  3. Adjacent atoms do not have formal charges of the same sign.
function calculateFormalCharge() { var v = parseFloat(document.getElementById('valenceElectrons').value); var n = parseFloat(document.getElementById('nonBondingElectrons').value); var b = parseFloat(document.getElementById('bondingElectrons').value); var resultBox = document.getElementById('fcResultBox'); var fcValueSpan = document.getElementById('fcValue'); var interpretation = document.getElementById('fcInterpretation'); if (isNaN(v) || isNaN(n) || isNaN(b)) { alert("Please enter valid numerical values for all fields."); return; } // Calculation: FC = V – N – (B/2) var fc = v – n – (b / 2); // Display result fcValueSpan.innerHTML = (fc > 0 ? "+" : "") + fc; resultBox.style.display = 'block'; // Basic interpretation logic if (fc === 0) { interpretation.innerHTML = "This atom is neutrally charged in this configuration."; } else if (fc < 0) { interpretation.innerHTML = "This atom has a surplus of electron density relative to its free state."; } else { interpretation.innerHTML = "This atom has a deficit of electron density relative to its free state."; } // Scroll to result for mobile users resultBox.scrollIntoView({ behavior: 'smooth', block: 'nearest' }); }

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