Here we have the periodic table showing only the valence, or outer electrons in each element. It is these outermost electrons that determine an element’s reactivity. Some patterns should stand out.

GCSE Combined Science Building blocks for understanding learning resources for adults, children, ... The periodic table - AQA Synergy. Mendeleev made an early periodic table.

2019 is the International Year of the Periodic Table. The person who typically gets credit for its creation is Dimitri Mendeleev. But there were many more chemists who should be recognized.