Today, the periodic table is organized by atomic number, which is the number of protons in the nucleus. But they didn’t know about protons then, so they organized everything by atomic weight.

Columns in the periodic table are called groups or families. Elements within the same group share similar properties because they have the same number of valence electrons (electrons in the ...

The perennially useful original Mendeleev periodic table has led to spinoffs, including for quantum dots. More stable nuclei are in the center, and they grow more deformed as you move outward.

This allowed elements to be placed with their chemical families. In 1871, Mendeleev published an updated version of his original Periodic Table, in which he switched the rows and columns.

The periodic table traditionally taught in textbooks, which organizes elements based on chemical traits such as reactivity, places helium in the rightmost column with the other less reactive elements.

Elements are organized on the periodic table by the number of protons they have. Of the 118 elements on the periodic table, 94 occur naturally. The remaining elements are artificially made.

It also determines their properties. Mendeleev’s periodic table of the elements is organized according to atomic weight: the combined number of protons and neutrons that make up its nucleus.

With those elements, the seventh row of the periodic table is now complete. Which would make element 118 a noble gas, if it actually existed for long enough to have a clearly defined state.

One in 5 Americans can't name a single element on the Periodic Table. Most Americans surveyed (59 percent) couldn't name more than 10 elements of the 118 that grace the Periodic Table.