The property which supports this statements is Multiplicative Identity Property of Real Numbers.
According to this property if any non-zero number is multiplied to 1, the result will be the same number. Because of this 1 is known as the multiplicative identity of the Real numbers.
8 because all elements after nitrogen have not only two energy levels, they also find it easier to just get rid of electrons than to absorb electrons to get to 8 electrons.