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 groups ...

Late 1600s – Dutch scientist Antonie van Leeuwenhoek constructed a microscope with a single spherical lens. It magnified up to ×275. 1800s - the optical quality of lenses increased and the microscopes ...