Elements in a group generally possess similar properties

Elements in a group generally possess similar properties, but elements along a period have different properties. How do you explain this statement ?

  1. Physical and chemical properties of elements are related to their electronic configurations, particularly the outershell configurations.
  2. Therefore, all the elements in a group should have similar chemical proper┬Čties.
  3. Similarly, across the table from left to right in any period, elements gets an increase in the atomic number by one unit between any two successive elements.
  4. Therefore, the electronic configuration of valence shell of any two elements in a period is not same. Due to this reason, elements along a period possess different chemical properties.