Periodic Trends: Ionization Energy

Supply energy and observe whether a valence electron escapes

Atom neutral

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Select an element

Na11

Sodium

Shells: 2, 8, 1

495.8IE kJ/mol

5.14eV/atom

1outer e⁻

Simulation speed1×

Ionization experiment

Energy supplied450 kJ/mol

0.52–207.29 eV per atom4.66 eV

Threshold: 495.8 kJ/mol

Ready: supply energy, then fire.

Compare two atoms

Quick investigations

Concept coach: why is one higher?

Energy and electron motion

━━ electron distance ━━ excess energy

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3D view controls

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Teacher / Demo tools

Custom nuclear charge+11

Quantum orbital probability view

The point cloud samples where an electron is likely to be detected. Colors show opposite wavefunction phases, not positive and negative charge.

Cloud samples500

Subshell energy diagram

Highlighted arrow: electron selected for removal.

Laser frequency and excitation

Wavelength266 nm

Frequency1127 THz

4.66photon eV

2.10excitation eV

0.00electron KE eV

At a matching internal energy, the electron moves to a higher subshell. At or above the ionization threshold, it escapes.

Successive ionizations and effective charge

0ion charge

1.00effective Z

495.8next IE

Successive values are measured for featured examples and educationally modeled for other elements.

External fields

Field strength50%

The electric field accelerates the negative electron opposite the field direction. The magnetic field curves its moving path through the Lorentz force.

Interactive periodic-table heat map

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Tap an element to load it in 3D.

Multi-property correlation plot

Tap a data point to load that element. Missing property values are omitted.

Periodic anomaly investigator

Choose an anomaly to highlight electron configuration and subshell stability.

Mystery element challenge

Start a challenge to receive successive ionization clues.

Classroom investigation tools

Guided lab worksheetEditable

The energy needed to remove the first electron

First ionization energy is the minimum energy needed to remove one electron from each atom in one mole of isolated gaseous atoms. The measured values below are real; the animated atom is a simplified probability-shell model.

Learning objectives

Predict the general direction of first-ionization-energy trends.
Connect nuclear charge, distance, and shielding to attraction.
Use an energy threshold to explain electron removal.
Explain important subshell and electron-pairing exceptions.

A reliable way to reason

Count occupied shells. More shells usually mean a farther, more shielded valence electron.
Compare proton number. Within the same period, more protons usually create stronger attraction.
Check the subshell. A new p subshell or paired p electrons can create an exception.
Predict removal difficulty. Stronger attraction means a higher ionization-energy threshold.

Why the trend occurs

Effective nuclear charge

Across a period, proton number rises while added electrons enter the same main shell. Attraction usually strengthens.

↔

Distance and shielding

Down a group, a new electron shell increases distance and inner electrons shield the valence electron, so removal becomes easier.

⚡

Threshold behavior

Below the ionization energy, the electron remains bound. Above it, the excess becomes kinetic energy of the separated electron.

Measured examples

Important exceptions

Boron is below beryllium: B loses a higher-energy 2p electron more easily than Be loses a filled 2s electron.
Oxygen is below nitrogen: paired 2p electrons repel, making one easier to remove; N has a stable half-filled 2p arrangement.
The same patterns recur for aluminum below magnesium and sulfur below phosphorus.

Scientific data sources

Neutral-atom ionization energies follow the NIST Atomic Spectra Database. Full-table ionization energy, atomic radius, electronegativity, and configurations are embedded from the PubChem Periodic Table dataset.

Suggested experiments

Choose Na, set energy just below its threshold, fire, then add 10 kJ/mol and retry.
Compare Li, Na, and K while watching shell number and threshold.
Compare Be with B and N with O to find where the smooth trend breaks.
Use noble gases and observe their unusually high thresholds.

Questions for exploration

Why is helium harder to ionize than hydrogen?
Why does a new period begin with a sharp drop?
How does excess supplied energy affect electron speed?

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