why are the eight elements in period three of the periodic table placed in the same period?Give 5 reasons why.

The periodic table is arranged in order of increasing
atomic number as you go across a period. It is also arranged according to the number of
electrons that will fit in a given energy level. So period 1 is also energy level one,
with only two electrons. Period 2 is energy level 2 with a maximum of 8 electrons. The
same is true for period 3,with room for 8 additional electrons.  Because there can only
be up to 8 more electrons in the third energy level, there is a maximum of 8 elements in
period 3. Once you get to element 19, the additional electrons move into the 4th energy
level - period 4.