What is the significance of the vertical columns in the periodic table?

Answer 1

An element's position in the Periodic Table from side to side relates to the number of electrons in the outer shell of an atom of that element. So an element (like Lithium or Sodium) in the left hand column - known as Group 1 - will have one electron in its outer shell. An element from the right hand column (like Neon or Krypton) - known as group 8 - will have eight electrons in its outer shell.

Some exceptions are:

Helium - although this falls in group 8, it has only two electrons in its outer shell.

The "Transition Metals" - These metals, which are the most familiar elemental metals like gold, silver, lead etc - have their own groupings, but two transition metals which share the same vertical column will have the same number of electrons in their outer shells.