Six elements of periodic table A, B, C, D, E and F have atomic numbers of 2, 12, 20, 18, 4 and 10 respectively (where A, B, C, D, E and F are not the chemical symbols of these elements). Based on this information, answer the following questions : Which of these elements belong to the same periods of the periodic table? Why?

Six elements of periodic table A, B, C, D, E and F have atomic numbers

1.	Six elements of periodic table A, B, C, D, E and F have atomic numbers of 2, 12, 20, 18, 4 and 10 respectively (where A, B, C, D, E and F are not the chemical symbols of these elements). Based on this information, answer the following questions : Which of these elements belong to the same periods of the periodic table? Why?
Answer» Solution :First of all, write the electronic configurations of all the given six elements as follows: (2) (i) Element B (2, 8, 2) and element D (2, 8, 8) belong to the third period because they both have 3 ELECTRON shells - K, L and M each. (ii) Element E (2, 2) and element F (2, 8) belong to the second period because they both have 2 electron shells - K and L each.