(a) List two advantages of adopting the atomic number of an element as the basis of classification of elements in the Modern Periodic Table.

(b) Write the electronic configurations of the elements X (atomic number 13) and Y (atomic number 20).

(a) The advantages of adopting the atomic number of an element as the basis of classification of elements in the Modern Periodic Table are :

1. Elements in the same group have same number of valence electrons. It correlates the position of the element with its electronic configuration clearly.

2. The completion of each period is more logical. Across a period as the atomic number increases the energy shells are gradually filled up until an inert gas configuration is reached.

(b) Electronic configuration of X(13) = 2, 8, 3 and Y(20) = 2, 8, 8, 2