An element 'P' has 3 valence electrons in its L - shell and an element 'Q' has 7 valence electrons in its M - shell. Using this information, answer the following questions:
(a) Identify the exact position of element 'Q' in terms of group and period in the Modern Periodic Table.
(b) The atomic radius of P is ............... (more/less) than that of Q.
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Element P has the L shell as its outermost shell with 3 valence electrons, so its configuration is 2, 3 (period 2). Element Q has the M shell as its outermost shell with 7 valence electrons, so its configuration is 2, 8, 7 (period 3).
(a) Element Q has 7 valence electrons, so it belongs to Group 17, and its outermost shell is the M (third) shell, so it belongs to Period 3.
Position of Q: Group 17, Period 3.
(b) The atomic radius of P is less than that of Q.
Element P has only two shells whereas Q has three shells. As the number of shells increases, the atomic radius increases. Hence, P (fewer shells) has a smaller atomic radius than Q.