Ionization Energy Calculator

Look up and compare ionization energies for elements. Calculate energy needed to remove electrons using Bohr model approximation for hydrogen-like ions. Analyze periodic trends.

⚗️ Atomic Structure📐 IE = Z²×13.6 eV/n² (H-like)🧪 Chemistry
Atomic number Z
Principal quantum number n
Effective nuclear charge Z_eff (optional, for multi-electron)
Please enter valid values.

Formula & Reference

VariableSymbolFormulaUnits
Ionization Energy Calculator—IE = Z²×13.6 eV/n² (H-like)eV or kJ/mol

Step-by-Step Examples

Example 1
Hydrogen Ground State

H: Z=1, n=1.

  • IE = 1^2 x 13.6/1^2 = 13.6 eV
  • = 13.6 x 96.485 = 1312 kJ/mol
✓ IE(H) = 13.6 eV = 1312 kJ/mol
Example 2
He-like Ion

He: Z=2, Z_eff ~ 1.7 (screening), n=1.

  • IE = (1.7)^2 x 13.6/1 = 2.89 x 13.6 = 39.3 eV
  • Actual He IE = 24.6 eV (Z_eff = sqrt(24.6/13.6) = 1.34)
✓ IE(He) = 24.6 eV (Z_eff = 1.34 accounting for electron shielding)
Example 3
Trends Across Period 2

Li: Z=3, Z_eff(2s)~1.3. F: Z=9, Z_eff(2p)~5.1.

  • IE(Li) = (1.3)^2 x 13.6/4 = 5.75 eV (act: 5.39)
  • IE(F) = (5.1)^2 x 13.6/4 = 88.5 kJ? No: 88.5/96.5x1000=882 kJ/mol (act: 1681)
  • Z_eff increases across period: IE increases
✓ IE generally increases across a period from left to right

Real-World Applications

⚗️
Periodic Trends
IE increases across periods (larger Z_eff) and down groups (higher n).
⚡
Plasma Chemistry
Ionization energies determine plasma composition and electron temperatures.
🧪
Thermochemistry
IE values are essential for Born-Haber cycle calculations of lattice energy.
💎
Mass Spectrometry
Electron ionization energy (typically 70 eV) chosen to exceed IE of most organic compounds.

Common Mistakes to Avoid

⚠️
Bohr model only exact for H-like ions

For multi-electron atoms: use effective nuclear charge Z_eff (from Slater rules or literature). Bohr model overestimates IE for multi-electron atoms.

⚠️
IE increases across a period

As Z increases across a period, electrons are in same shell (similar shielding) but nucleus charge grows. Z_eff increases, IE increases.

⚠️
Exceptions to periodic trend

B (IE lower than Be): new 2p subshell, less penetrating. O (IE lower than N): paired electrons in 2p repel, easier to remove one.

Frequently Asked Questions

What is ionization energy? ▾
Energy to remove one mole of electrons from one mole of gaseous atoms. Always positive (endothermic). Larger IE: harder to remove electron (more stable).
What are periodic trends in IE? ▾
Increases left to right across period (increasing Z_eff). Decreases down group (increasing n). Exceptions: Group 13 lower than Group 2; Group 16 lower than Group 15.
What is effective nuclear charge? ▾
Z_eff = Z - sigma (screening constant). Inner electrons partially shield outer electrons from full nuclear charge. Slater rules estimate sigma.
What is successive ionization energy? ▾
IE1: remove first electron. IE2: remove second (much harder). Large jump in IE indicates valence electron count. Na: IE1=496, IE2=4562 kJ/mol (large jump after 1 valence electron).
What is electron affinity? ▾
Energy released when an atom gains one electron: X + e^- to X^-. Opposite of IE. Highly negative EA (large release) for halogens (F, Cl).

Related Chemistry Calculators

⚗️ Electron Configuration⚗️ Electronegativity⚗️ Quantum Numbers🧪 Lattice Energy☢️ Nuclear Symbol

Formula Explorer connections

Interpretation: This relationship uses electronic structure, bonding or molecular geometry to predict a chemical property or structural descriptor. Assumption: The model may be an approximation; resonance, solvent, coordination environment, conformation and experimental conditions can affect real molecules.

Solvent Polarity Index Calculator →Protecting Group Selection Calculator →Quantum Numbers Calculator →Chemistry Formula Explorer →