Lavoisier wrote the first ever chemistry textbook called the Elementary Treatise of Chemistry. The book contained a list of elements, the most recent theories and laws of chemistry including the Conservation of Mass.
Law of Triads
Groups of three elements could be grouped together based off of appearance and properties.
John Newlands was the first scientist to propose a periodic table organised by atomic mass.
Law of octaves
John Newlands proposed the law of octaves which stated that any element will act similarly to the element eight places after it.
1864 - 1870
Meyer wrote a book illustrating the fundamental aspects of chemistry, called Die modernen Theorien der Chemie (or Modern Chemical Theory) in 1864. Meyer began working on a Periodic Table in 1868, and he released his research in 1870.
Dimitri Mendeleev published a periodic table that allowed known elements to be grouped according to their properties and atomic weight.
Plutonium is a radioactive element which first found in 1940 by Glenn Seaborg and his team Arthur Wahl, Joseph Kennedy, and Edwin McMillan.