With these elements, the atomic weight of the longest-lived isotope gets listed on the periodic table, according to the International Union of Pure and Applied Chemistry (IUPAC).

Dmitri Mendeleev (1834-1907) and Lothar Meyer (1830-1895) independently developed the Periodic Law in 1869, observing periodic similarities in element properties when arranged by atomic weight.

We learn the periodic table as the elements arranged according to the atomic number, which is an integer, a whole number. That's the number of protons in an atom of that element.

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.

Episode 8 - Groups in the periodic table In this episode, Dr Sunayana Bhargava and Tulela Pea look at groups 1, 7 and 0 of the periodic table, exploring the properties of the elements in each group.

For the first time in history, a change will be made to the atomic weights of some elements listed on the Periodic table of the chemical elements posted on walls of chemistry classrooms and on the ...

Atomic weights of 10 elements on periodic table about to make an historic change Date: December 16, 2010 Source: University of Calgary Summary: For the first time in history, a change will be made ...

For example, sulfur is commonly known to have a standard atomic weight of 32.065, but its real atomic weight can be anywhere between 32.059 and 32.076, depending on where the element is found.