Rules for Identification of Group, Period and Block

Rules for Identification of 

Group, Period and Block

1. If valence shell electronic configuration of an element is “ns^x np^y”  then element is a representative element of group A whose:

2. If valence shell electronic configuration of element lies in d-orbital, then element is outer transition metal belongs to sub-group B. (In transition elements, the outer shell consists of ns and (n–1)d orbital).

3. If 4f – orbital is filling, element is Lanthanide of period 6 of f-block. e.g.

4. If 5f – orbital is filling, element is actinide of period 7 of f-block.

Summary of Rules for Identification of Group, Period and Block

Prediction of Period
The period of an element corresponds to the principal quantum number of the valence shell.

Prediction of Block
The block of an element corresponds to the type of valence orbital or highest energy orbital (out of s, p, d and f) of the valence shell which receives the last electron.

Prediction of Group
The group of an element is equal to the total number of electrons in the valence shell or and penultimate shell (i.e. total number of valence electrons). Group number depends on block:

(a) For s-block elements, group number is equal to the number of valence electrons in s-orbital.

(b) For p-block elements, group number is equal to the number of electrons in ‘s’ and ‘p-orbitals’ (or 10 + number of valence electrons in the valence shell or 12 + number of “p” electrons in the valence shell).

(c) For d-block elements, group number is equal to the number of electrons in “ns” & “(n-1)d- orbitals”

(d) For f-block elements; group number is always 3 or III (or no group).


5. Summary

Q1. Give the electronic configuration of elements having atomic number 6, 15, 29, 48, 59. State block, period and group of each.

Answer

Atomic No. 6 Element  = Z  =  6  =  6e^-  =  1s², 2s²  2p²

                                                                            Valence Shell

1.  Since valence shell configuration ends in p-orbital, therefore, this element is the representative element belongs to p-block.

2. Since principal quantum number corresponds to period number thus the period of this element will be 2.

3.  Since valence shell configuration is 2s² 2p² (Total valence electron is 4), therefore, Group is IVA

Summary 

Atomic No. 15  Element = Z  =  15  =  15e^- = 1s²,  2s²  2p⁶, 3s² 3p³

                                                                                                                           Valence Shell

1. Since valence shell configuration is in p-orbital, therefore, this element is the representative element belongs to p-block.
2. Since principal quantum number corresponds to period number, thus the period of this element

3. Since total valence electrons are 5 (3s² 3p³), therefore, Group is VA.

Summary

Q2. Identify the Group, Period and Block, with electronic configuration

Answer

(a)        3s²  3p⁶,  4s¹

(i) Since ‘s’ orbital is the outermost orbital, it is a representative element belongs to ‘s’ block.

(ii) Since valence shell configuration is 4s¹, so Group is I-A.

(iii)  Since highest ‘n’ corresponds to Period, thus Period is 4.

 

(b)       3s²  3p⁵

(i) Since last electron lies in ‘p’ orbital, it is a representative element belongs to p-block.

(ii)  Since valence shell configuration is 3s² 3p⁵ (Total valence electrons are 7) so Group is VIIA.

(iii) Since ‘highest n’ corresponds to Period, thus Period is 3.

 

(c)        4s²  4p⁶

(i)  Since s and p orbitals are completely filled, it is a noble gas.

(ii) Since total valence electrons are 8 (4s²  4p⁶), so Group is VIIIA.

(iii)  Since ‘highest n’ corresponds to Period, thus Period is 4.

 

(d)       4d¹  5s²

(i)  Since last electron lies in ‘d’ orbital, it is outer transition metal belongs to d-block.

(ii)  Since valence shell configuration is 4d¹ 5p² (Total valence electrons are 3) so Group is IIIB.

(iii) Since ‘highest n’ corresponds to Period, thus Period is 5.

 

(e) 3d¹⁰ 4s²  4p³

(i) Since last electron lies in ‘p’ orbital, it is a representative element belongs to p-block.

(ii)  Since valence shell configuration is 3d¹⁰ 4s² 4p³ (Total valence electrons are 5) so Group is VA.

(iii) Since highest ‘n’ corresponds to Period, thus Period is 4.

 

(f)        2s² 2p⁶

(i) Since s and p orbitals are completely filled, it is a noble gas.

(ii) Since total valence electrons are 8 (2s² 2p⁶), so Group is VIIIA.

(iii) Since ‘highest n’ corresponds to Period, thus Period is 2.

Q3. Give the E.C. and identify group, period and block of elements with following atomic numbers: 7, 9, 11,13, 18, 20, 21, 24, 26, 29, 30, 34