The periodic law states “When elements are arranged in order of increasing atomic number, there is a periodic repetition of their chemical and physical properties.”

What eventually happened to these gaps? Mendeleev left gaps in between his periodic tabel as he knew that no exisiting (undiscovered) element could fill the gap and that there has to be an element. The gaps were eventually filled when new elements were discovered.

The Periodic Law states that the physical and chemical properties of the elements recur in a systematic and predictable way when the elements are arranged in order of increasing atomic number.

The modern periodic table of the elements contains 18 groups, or vertical columns. Elements in a group have similar chemical and physical properties because they have the same number of outer electrons. Scientists in the United States and Europe now use different titles to refer to the same groups.

Periodicity is the fact of something happening at regularly-spaced periods of time. An example of periodicity is the full moon happening every 29.5 days. The tendency, quality, or fact of recurring at regular intervals. The occurrence of similar properties in elements occupying similar positions in the periodic table.

The periodical repetition of similar properties of the elements after certain regular intervals when the elements are arranged in order of increasing atomic number is called periodicity.

Answer: Repitition of properties after certain intervals is called periodicity of properties. If elements are arranged in increasing order of atomic number in the periodic table then elements repeat its properties after a definite interval.

The modern periodic table is based on the electronic configuration of the elements. The properties which are directly or indirectly related to their electronic configuration and which show a regular gradation when we move from left to right in a period or from top to bottom in a group are called periodic properties.