The periodic table on the website of the International Union of Pure and Applied Chemistry avoids making a decision about whether La and Ac or Lu and Lr are group 3 elements.

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.

The organization of the periodic table reveals an element’s behaviors and characteristics: from atomic size, density and abundance, to how it would likely interact with others. Elements 101 Everything ...

Three reasons why the periodic table needs a redesign. ... By element 57, lanthanum, the electrons begin to enter a new type of orbital, an f-orbital. To account for this, ...

The periodic table of chemical elements, often called the periodic table, organizes all discovered chemical elements in rows (called periods) and columns (called groups) according to increasing atomic ...

Since the invention of the periodic table 150 years ago this month, scientists have worked to fill in the rows of elements and make sense of their properties. But researchers have also pursued a ...

Predictive power. Gallium. Mendeleev left blank spaces in his original periodic table so that he could properly line up the known elements. Gallium, element 31, was his first gap to be filled, in ...