they are called periods
The horizontal rows are called periods
noble gases
it took mendleev FROM 1872 TO 1871. He figured it out in a dream that he had had whilst trying to figure out the problem
In addition to hydrogen, all elements in Group I of the periodic table have one valence electron. They are lithium, sodium, potassium, rubidium, cesium, and francium. The farther you move right on the periodic table the more valence electrons. For example, elements in Group VII have 8 valence electrons except helium.
The Periodic Table is arranged like it is for a specific reason. It is probably called the Periodic Table because it is made up of "periods" or horizontal rows.
period
The Communist's Periodic Table of Elements:)Couldn't Resist
they are called periods
The horizontal rows are called periods
Chemists call this the periodic table of elements.
The Periodic Table of Elements
The elements are arranged in what is called the periodic table.
A period
The "Periodic Table".
A group of elements in the periodic table is called metals.
Periodic Table