What Is Periodicity on the Periodic Table?

Periodicity is one of the most fundamental aspects of the periodic table of the elements. Here is an explanation of what periodicity is and a look at the periodic properties.

What Is Periodicity?

Periodicity refers to the recurring trends that are seen in the element properties. These trends became apparent to Russian chemist Dmitri Mendeleev (1834–1907) when he arranged the elements in a table in order of increasing mass. Based on the properties that were displayed by the known elements, Mendeleev was able to predict where there were "holes" in his table, or elements yet to be discovered.

The modern periodic table is very similar to Mendeleev's table, but elements today are ordered by increasing atomic number, which reflects the number of protons in an atom. There aren't any "undiscovered" elements, although new elements can be created that have even higher numbers of protons.

What Are the Periodic Properties?

The periodic properties are:

1. Ionization energy: the energy required to remove an electron from an ion or gaseous atom
2. Atomic radius: half the distance between the centers of two atoms that are touching each other
3. Electronegativity: the measure of the ability of an atom to form a chemical bond
4. Electron affinity: the ability of an atom to accept an electron

Trends or Periodicity

The periodicity of these properties follows trends as you move across a row or period of the periodic table or down a column or group:

Moving Left → Right

• Ionization Energy Increases
• Electronegativity Increases
• Atomic Radius Decreases

Moving Top → Bottom

• Ionization Energy Decreases
• Electronegativity Decreases
• Atomic Radius Increases