Before 1937, all naturally occuring elements had been discovered, but no one had found any trace of element 43. Chemists were still able to predict the chemical properties of this element (now called technetium), which is widely used today for diagtnosing medical problems. How were these predictions possible? Which elements would you expect to be similar to technetium?

Answer 1

The periodic table is a chart that arranges the elements in rows and columns. Those elements in the same column have similar chemical/physical properties. Here is a link that gives more detail.
http://chemistry.about.com/library/blperiodictable.htm