Which element has the lowest ionization energy?
Quick Answer
Francium is generally expected to have the lowest first ionization energy, but because it is extremely rare and radioactive, this is based on theory rather than extensive direct measurement. Cesium is very close and is the most commonly referenced practical example.
The Full Story
Francium is predicted to have the lowest first ionization energy among the elements because of periodic trends, though direct measurements are difficult due to its scarcity and short half-life. Cesium is the closest well-studied element and is often used in classroom comparisons because it is more accessible. Both are alkali metals, a family known for easily losing their outermost electron. This makes them some of the most chemically reactive metals on the periodic table.
Key Facts
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Suggested video title for this topic:
"The easiest atom to strip an electron from"