Question

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How does number of (i) valence electrons (ii) valency;
vary on moving from left to right :
(a) in the second period of a periodic table ?
(b) in the third period of a periodic table ?
​

Answer 1

(i) The number of valence electrons increases by one as we move from left to right in a period. The group number 1 and 2 have 1 and 2 valence electrons respectively while group 13 to 18 have group number minus 10 = valence electrons. So, group 13 to 18 have 3, 4, 5, 6, 7 and 8 valence electrons respectively.

(ii) Valency is determined by the number of valence electrons. For elements belonging to group 1, 2 and 13, the valency is equal to the number of valence electrons, so their valency is 1, 2 and 3 respectively.

Since the elements in group 14 to 17 needs to gain electrons to complete their octet configuration. Their valency is 8 minus the number of valence electrons. So their valencies are 4, 3, 2 and 1 respectively.

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