Meadowvale Secondary School

SCH 3U

The Periodic Table & The Development of Atomic Theory Dimitri Mendeleev – Russian Chemist In 1869 about 63 different elements had been identified. Mendeleev wrote their name, mass, density, melting points and other physical and chemical properties on individual cards. Then he played “chemical solitaire”, arranging the cards in different ways to see if he could find a pattern. He organized his table by arranging the elements according to increasing atomic mass. When an element appeared to have repeating properties he started a new row. Eventually he found that elements with similar properties fit into the same vertical columns. When Mendeleev came to a place on his table where no known element would fit in, he used a blank card. By examining the properties of the surrounding elements he accurately predicted the existence and properties of 3 unknown elem