How the positions of elements in the periodic table

How the positions of elements in the periodic table help you to predict its chemical properties? Explain with an example.

  1. In periodic table, I group elements have valency 1 and for second group elements have valency.
  2. Similarly every group elements have definite valencies, so we can predict how they can react with different elements and form compounds.
    For example, alkali metals react with oxygen, hydrogen and chlorine like this,

This can be predicted by using valency from periodic table.