For all their nobility, elements of group 18 have lived in relative obscurity. In 1869, Mendeleev's first periodic table did not include them, as closed-shell elements remained undiscovered until ...

Bohr's theory that electrons existed in set orbits around the nucleus was the key to the periodic repetition of properties of the elements. The shells in which electrons orbit have different ...

Elements in group 1 and group 2 are metals. Atoms of group 1 elements have one electron in their outer shell, and atoms of group 2 elements have two electrons in their outer shell. Elements in ...

Bohr's theory that electrons existed in set orbits around the nucleus was the key to the periodic repetition of properties of the elements. The shells in which electrons orbit have different ...