Chemistry · Periodic table

Periodic Trends Explorer

Pick an element with the slider or by selecting it in the periodic table, then choose which property to color the table by: covalent radius, first ionization energy, electronegativity, or effective nuclear charge. Elements 1 to 36 are shown.

The effective nuclear charge, Zeff, is calculated on the page from the element's electron configuration with Slater's rules. Compare Zeff with the other three properties, across a period and down a group, to see which trends it explains.

Model notes

Covalent radii are the Cordero 2008 set, in picometers. First ionization energies are in kJ/mol. Electronegativities are on the Pauling scale, and He, Ne, and Ar have no accepted value. Values come from standard reference tables, so check any number you need to cite against your textbook or a data source such as NIST.
Zeff here uses Slater's rules for the outermost electron. It is a useful estimate and it is not exact. Methods that fit the wave functions, such as Clementi and Raimondi's, give somewhat different numbers, and they agree on the trends.
Covalent radius has no single correct value for noble gases and for elements that form different kinds of bonds. Treat differences of a few picometers as noise.
For transition metals the outermost electron is in the 4s subshell, and the 3d electrons shield it by 0.85 each, so Zeff changes only slowly across the row.

Sources

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