How do the number of electrons in the second energy shell of an atom change going across period 2 in the periodic table? a. the number of electrons increases by 1, from left to right. b. atoms in period 2 do not have a second energy shell, instead the first energy shell increases in electrons from left to right. c. the number of electrons in the second energy shell is full, the number of electrons in the third energy shell increase by 1. d. the number of electrons increases by 1, from right to left.

The answer should be A, the number of electrons increases by 1, from left to right.

Across the periods (horizontal direction) in periodic table, each element has one more electron then the one before it. The number of period determines the number of occupied electron shells of the elements in that period. Which means, period 1 elements have 1 occupied electron shell, period 2 has 2, period 3 has 3 etc.

Therefore, the answer is A, we always go from left to right, and plus since period 2 elements only have 2 occupied electrons so their 2nd electron shell electrons must increase throughout the period.