How many horizontal rows (periods) are in the modern periodic table?

Periodic Table: Classifications — Who is credited with first publishing a periodic table that organized the elements into a repeating pattern of properties?

Who is most commonly credited with creating the first widely recognized periodic table of elements based on recurring (periodic) properties?

Periodic Table: Classifications — Who is most commonly credited with creating the first widely recognized periodic table?

Periodic Table: Classifications — Who is credited with creating the first widely recognized periodic table that arranged elements in order of increasing atomic mass and predicted properties of undiscovered elements?

How are elements on the periodic table arranged?

How are metals primarily designated in the periodic table based on their location?

Periodic Table: Classifications — How did Dmitri Mendeleev originally organize the periodic table?

How are the elements arranged in the modern periodic table?