CBSE Class 10 Science 2018 · Paper 31(B) · Question 8

Periodic Classification of Elements 3 marks Medium

Consider the following five elements of the modern periodic table (atomic number of each is given in the parenthesis) : P(4), Q(9), R(14), S(19), T(20) Giving reason answer the following questions :

(i)Which two elements belong to the same period ?
(ii)Which two elements belong to the same group ?
(iii)Which element has seven electrons in its outermost shell ? Write the formula of its halide.

Answer

P and Q share a period, P and T a group; Q has seven outer electrons and forms halides $SQ$ and $TQ_{2}$ .

Electronic configurations: P (4) 2, 2; Q (9) 2, 7; R (14) 2, 8, 4; S (19) 2, 8, 8, 1; T (20) 2, 8, 8, 2. (i) P and Q belong to the same period (period 2), because both have two shells. S and T are also in one period (period 4), with four shells each. (ii) P and T belong to the same group (group 2), because both have two valence electrons. (iii) Q (2, 7) has seven electrons in its outermost shell. It is a halogen with valency 1, so it forms halides with the metals in the list, for example

SQ

(with S, valency 1) and

TQ_{2}

(with T, valency 2).

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CBSE Class 10 Science 2018 · Paper 31(B) · Question 8

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