Enter the number of the metal’s d electrons, the number of the ligands’ s electrons, the number of the ligands’ p electrons, and the number of electrons involved in metal-ligand bonding into the calculator to determine the total number of electrons.

18 Electron Rule Formula

The following formula is used to calculate the 18 Electron Rule. 

E = d + s + p + b

Variables:

  • E is the total number of electrons (should be 18 for stability)
  • d is the number of the metal’s d electrons
  • s is the number of the ligands’ s electrons
  • p is the number of the ligands’ p electrons
  • b is the number of electrons involved in metal-ligand bonding

To calculate the total number of electrons, add the number of the metal’s d electrons, the number of the ligands’ s electrons, the number of the ligands’ p electrons, and the number of electrons involved in metal-ligand bonding. The total should ideally be 18 for the complex to be stable according to the 18 Electron Rule.

What is an 18 Electron Rule?

The 18 Electron Rule is a chemical rule of thumb used primarily for predicting and explaining formulas and structures of transition metal complexes, particularly organometallic compounds. The rule is based on the fact that the shells of transition metals are most stable when they contain 18 electrons. This includes the metal’s d electrons, the s and p electrons of the ligands, and any electrons involved in metal-ligand bonding. The rule is useful in the design and understanding of catalysts.

How to Calculate 18 Electron Rule?

The following steps outline how to calculate the 18 Electron Rule.

  1. First, determine the number of the metal’s d electrons (d).
  2. Next, determine the number of the ligands’ s electrons (s).
  3. Next, determine the number of the ligands’ p electrons (p).
  4. Next, determine the number of electrons involved in metal-ligand bonding (b).
  5. Finally, calculate the total number of electrons (E) using the formula E = d + s + p + b.
  6. After inserting the values for d, s, p, and b, calculate the result to determine if it equals 18 for stability.

Example Problem:

Use the following variables as an example problem to test your knowledge.

d = 8

s = 2

p = 6

b = 2

Calculate the total number of electrons (E) using the formula E = d + s + p + b.