The Development of the Periodic Table Date Scientist 1787 The Development of the Periodic Table Observation/discovery Date Classified known elements into metals and non-metals, based on their physical and chemical properties 1787 Dalton Scientist Classified known elements into metals and non-metals, based on their physical and chemical properties Dalton Triads – similarities exist in sets of three elements Triads – similarities exist in sets of three elements Newlands 1869 Newlands 1869 Mosely Observation/discovery Mosely ANSWER The Development of the Periodic Table Date Scientist Observation/discovery 1787 Lavoisier Classified known elements into metals and non-metals, based on their physical and chemical properties 1808 Dalton Elements are made up of small particles called atoms 1829 Dobereimer Triads – similarities exist in sets of three elements 1863 Newlands Law of Octaves – if elements were placed in order of increasing atomic mass, there was a repetition or periodicity in every eights element 1869 Mendeleev Elements arranged in increasing atomic mass demonstrated similar physical and chemical properties occurring at regular intervals 1914 Mosely Elements arranged in order of increasing atomic number, similar chemical properties occur periodically