1.15    deduce the number of outer electrons in a main group element from its position in the Periodic Table.

The number of electrons in the outer shell of an element = the group it is in.

Look at Si in the diagram of the Periodic Table above. Its electronic configuration is 2,8,4. From that we can deduce it is in Group 4. We can also deduce it is in the 3rd Period as it has 3 occupied electron shells (energy levels).

Group 0 is sometimes called Group 8. You can either argue that the outer electron shells of the elements have 8 electrons (apart from Neon, which has only 2) or that the elements don’t make compounds (hence Group 0).