On 17 February 1869, Russian chemist Dmitri Mendeleev jotted down the symbols for the chemical elements, putting them in order according to their atomic weights and inventing the periodic table.

Since the 19th century, more elements have been discovered that fit these gaps, further confirming that Mendeleev’s understanding was correct. Image caption, The element germanium was discovered ...

Since the 19th century, more elements have been discovered that fit these gaps, further confirming that Mendeleev’s understanding was correct. Image caption, The element germanium was discovered ...