So you can classify the elements into groups.
it is 56 because you round it of and it used to be 55.85
Iron.
Periodical chart
Calcium
about 106 are on a periodic table for the very time being
Because it is an element.
The periodical beeping was driving us insane.
Na is an element found on the periodical table. It is the chemical symbol for Sodium.
Dmitri Mendeleev
A periodical index is a research tool that is used to locate articles in professional publications.
Sulphur/ Sulfur --> S (in capital letter) in the periodic table
For halogens this is the only way to react as oxidant.