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Ionisation energy
Intermediate
Energy needed to remove an electron.
Energy needed to remove an electron: 13.6 eV for hydrogen, 24.6 eV for helium (first). It rises across periods and drops down groups.
Alkali metals have low IE (~4–5 eV).
Successive ionisations get harder.
In more detail
Ionisation energy is the energy needed to remove an electron from an atom. For hydrogen it is 13.6 electron volts.
Real-world uses
- Chemists compare ionisation energies to predict chemical behaviour.
- Gas discharge lamps depend on ionisation energies.
- Plasma physicists and astronomers estimate the energy needed to strip electrons from atoms in hot gases.
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Frequently asked questions
Which atom has the highest ionisation energy?
Helium, which has a very tightly bound pair of electrons.
Why does ionisation energy vary?
It depends on nuclear charge and electron shielding.
What is the ionisation energy of hydrogen?
About 13.6 electron volts, the energy needed to remove its single electron from the ground state.
Related topics in Atomic & Nuclear Physics
Hydrogen spectrum · Rydberg constant · Absorption and emission spectra · Franck–Hertz experiment · Characteristic X-rays · Continuous X-ray spectrum