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?

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

The predictions of the chemical properties of element 43, now known as technetium, were possible because of the periodic table and the understanding of periodic trends in chemical elements. The periodic table is an arrangement of elements based on their atomic number (number of protons), electronic configuration, and recurring chemical properties.

By examining the elements surrounding the empty spot for element 43 in the periodic table, chemists noticed a pattern of elements with similar properties. They noticed that elements in the same column, called a group or family, tend to have similar chemical behavior because they have the same number of valence electrons. Valence electrons are the electrons in the outermost energy level of an atom, and they play a key role in determining the chemical properties of an element.

Technetium is located in group 7 of the periodic table, also known as the transition metals or the manganese group. Chemists predicted that technetium would share similarities with its neighboring elements in this group, such as manganese (Mn), technetium (Tc), and rhenium (Re). These elements are expected to have similar chemical properties, including reactivity, due to their similar electron configurations and valence electrons.

It is important to note that while predictions could be made based on the periodic trends, the actual properties of technetium had to be experimentally confirmed once it was synthesized.