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

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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.

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