Ionization energy increases across a period.

the verdict

SUPPORTED

the evidence backs this

Recorded sources

6 sources for · 1 against

Counts group repeated records of the same source within each side. They do not measure evidence strength or source independence.

Is it true that ionization energy increases across a period?

Yes. Multiple reference sources state that first ionization energy generally increases from left to right across a period, with some noting exceptions such as aluminum and sulfur. One encyclopedia snippet appears to state the opposite, but the weight of sources supports the general trend.

Verdict: SUPPORTED · 6 sources for, 1 against · Last checked 17 Oct 2026

The private library was unavailable for some searches in this check. Missing library results are not evidence against the claim.

Evidence for · 6

Ionization energy

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Ionization energy. (n.d.). en.wikipedia.org. https://en.wikipedia.org/wiki/Ionization_energy

Evidence against · 1

Macmillan Encyclopedia of Chemistry

1997

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Lagowski, J. J. (1997). Macmillan Encyclopedia of Chemistry. books.google.com. http://books.google.com/books?id=kQ1LAQAAIAAJ&dq=Ionization+energy+increases+across+a+period.&hl=&as_pt=BOOKS&source=gbs_api

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More for · 5

Ionization

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Ionization. (n.d.). en.wikipedia.org. https://en.wikipedia.org/wiki/Ionization

A Noble-Gas-Centered Coordinate for Within-Period Ionization Energy Trends and Subshell Anomalies

2026

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Washburn, J., Simons, M., & Allahyarov, E. (2026). A Noble-Gas-Centered Coordinate for Within-Period Ionization Energy Trends and Subshell Anomalies. doi.org. https://doi.org/10.26434/chemrxiv.15002361/v1

SAT Subject Test Chemistry

2017

Get citation

Prep, K. T. (2017). SAT Subject Test Chemistry. books.google.com. http://books.google.com/books?id=QDSzCwAAQBAJ&dq=Ionization+energy+increases+across+a+period.&hl=&as_pt=BOOKS&source=gbs_api

Ionization Energies of Lanthanides

2010

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F., L. P. & C., S. B. (2010). Ionization Energies of Lanthanides. eric.ed.gov. https://doi.org/10.1021/ed100215q

Chemistry

1975

Get citation

Yoder, C. H., Suydam, F. H., & Snavely, F. A. (1975). Chemistry. books.google.com. http://books.google.com/books?id=PaImAQAAMAAJ&dq=Ionization+energy+increases+across+a+period.&hl=&as_pt=BOOKS&source=gbs_api

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