Valency of an element is determined by the number of valence electrons present in the outermost
shell of its atom. Valencies remain same in a group, due to this reason elements in a group show similar
properties. Valency increases from 1 to 4 and then decreases to zero in a period. Due to this reason chemical
properties vary in a period.
On the basis of above information answer the following questions:
(i) What is the valency of an element placed in group number 15.
(ii) Comment on the chemical property of anelement having valency zero.
(iii) Three different elements X, Y, Z have atomic numbers 11, 17, 13 respectively. Arrange
these elements in increasing order of their valencies.
(iv) Based on question (iii) above, which is most electro-positive and most electro-negative
element among X, Y, Z.
Answers
1)Group 15 (VA) contains nitrogen, phosphorous, arsenic, antimony, and bismuth. Elements in Group 15 have five valence electrons. Because the elements can either gain three electrons or lose five to gain a stable configuration, they more often form covalent compounds unless bonded to an active metal.
2)The first element helium (He) has only one shell and has maximum of two electrons in the only shell (K-shell) which it has. This means that the atoms of all the three elements donot have any range to either lose or gain electrons. Therefore they show zero valencies .
3)Three elements 'X', 'Y' and 'Z' having atomic numbers 7, 8 and 9 are nitrogen, oxygen and fluorine respectively. The atomic size decreases from left to right in a period in the modern periodic table. Hence, the decreasing order of their atomic radii is N>O>F.
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