☰
✕

Classification of Elements and Periodicity in Properties
Question
Wired Faculty App

The valence of representative elements is either equal to the number of valence electrons or eight minus the number. What is the basis of their rule?

Answer

The electrons present in the valence shell (outermost shell) are called valence electrons and their number determines the valency of the element. It has been found that in the case of representative elements (s-and p-block elements), the valency of an element is either equal to the number of valence electrons or eight minus the number of valence electrons, e.g. consider the hydrides of 2nd period i.e. groups 1,2, 13, 14, 15, 16, 17.

Group 1 2 13 14 15 16 17
Compounds LiH BeH2 BH3 CH4 NH3 H2O HF
No. of valence electrons  1 2 3 4 5 6 7
Valency of element 1 2 3 4 8-5 =3 8-6 =2 8-7 =1

From the above table, it is clear that valency of the representative elements of groups 1, 2, 13 and 14 is equal to the number of valence electrons. But the valency of representative elements of group 15, 16 and 17 is equal to eight minus number of valence electrons.

The valency of any element is the number of electrons which it loses, joins or shares with other atoms to attain the nearest inert gas configuration. The elements of groups 1, 2 and 13 lose 1, 2 and 3 electrons respectively to attain the nearest noble gas configuration. Thus, the valency of the elements of groups 1, 2 and 13 is equal to the number of their valence electrons. The elements of group 14 have four electrons in their respective valence shells and thus attain noble gas configuration only by sharing with four more electrons of other atoms. Therefore, the valency of elements of group 14 is also equal to the number of their valence electrons.

The elements of group 15, 16 and 17 have 5, 6 and 7 electrons in their respective valence shells and hence they acquire 3 (8-5), 2 (8-6) and 1 (8-7) electrons either by gaining or sharing electrons from other atoms to attain the nearest inert gas configuration. Thus, the valency of the elements of groups 15, 16 and 17 is equal to eight minus the number of electrons in their respective valence shells.

Sponsor Area

Some More Questions From Classification of Elements and Periodicity in Properties Chapter

How many elements are present in:
(i) second period    
(ii) fourth period    
(iii) sixth period?

What is the name given to the s-block elements?

To which block the element with outer electronic configuration 4s23d10 belongs?

Why are there 10 elements in each series of d-block?

In terms of electronic configuration,
what is common in a given period and group?

Give the general electronic configuration of
(i) Transition elements     (ii) Inner transition elements.

Name the group and period to which an element with Z = 15 belongs ?

What are the advantages of periodic classification of elements?

In the modern periodic table, the period indicates the value of:
(a) atomic number
(b) atomic mass
(c) principal quantum number
(d) azimuthal quantum number.

Which of the following statements related to the modern periodic table is incorrect?
(a) The p-block has 6 columns, because a maximum of 6 electrons can occupy all the orbitals in a p-shell.

(b) The d-block has 8 columns, because a maximum of 8 electrons can occupy all the orbitals in a d-subshell.

(c) Each block contains a number of columns equal to the number of electrons that can occupy that subshell.

(d) The block indicates value of azimuthal quantum number (l) for the last subshell that received electrons in building up the electronic configuration.