CBSE Class 10 Science 2017 · Paper 31/1/C · Question 13
Write the electronic configurations of two elements P (atomic number 17) and Q (atomic number 19) and determine their group numbers and period numbers in the Modern Periodic Table.
Answer
P (chlorine) is : period 3, group 17; Q (potassium) is : period 4, group 1.
P (atomic number 17): K, L, M . It has three shells, so it is in period 3; it has valence electrons, so it is in group 17. (P is chlorine.)
Q (atomic number 19): K, L, M, N . It has four shells, so it is in period 4; it has valence electron, so it is in group 1. (Q is potassium.)
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