The Periodic Table

How to Use It…

And Why Would I Ever Use It…

Who Made This Thing Anyway?

• In 1829, J.W. Dobereiner tried to classify elements into various groups based on some chemical and physical properties.

• He called these groups Triads…since they were in groups of 3.

• When he did this he found that the middle element ended up with an atomic mass that was about the average of the other 2.

More on Dobereiner

• While Mr. D’s triads worked great (and still are accurate) there was a more important discovery…

• His work helped to show that atomic mass was somehow related to the properties of an element.

Enter Another Dead Guy…

• In 1869, while working as a professor in Russia, Dmitri Mendeleev, developed what he called a periodic table of the elements.

• He noticed that when he put the elements in order of increasing atomic mass, that the elements properties repeated in an orderly way.

So Really How Good Was His Table…

• Mendeleev’s table was so good at predicting properties of elements at certain atomic masses…that he left blank spaces in the table where he thought elements should be…

• In later years, those elements were indeed discovered!

Mendeleev Made a Table…
So What!

• His insight into the periodicity of the elements was one of the greatest contributions to chemistry…

His Table Is Similar to Today’s

Some Differences Today