Cambrian shell fossils reveal predator-prey battles shaped evolution, as predators attacked and prey adapted by developing ...

With a heavy nucleus (79 protons) and a lone electron in its outermost electron shell, gold should have fairly similar ...

Elements in the same horizontal row are in the same period. The periods are numbered from top to bottom. The period number is the same as the number of occupied electron shells.

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 ...