What Is Periodicity on the Periodic Table?

Understanding Periodicity

Periodicity
The elements are arranged to display periodicity on the periodic table. Mirek2 / Wikimedia Commons

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 Mendeleev when he arranged the elements 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 today elements 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 - 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 - measure of the ability of an atom to form a chemical bond
  4. electron affinity - 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

Moving Top → Bottom

  • Ionization Energy Decreases
  • Electronegativity Decreases
  • Atomic Radius Increases

More about the Periodic Table

Periodic Table Study Guide
Mendeleev's Original Periodic Table
Periodic Table Trends