• AglaSem
  • Schools
  • Admission
  • Career
  • News
  • Hindi
  • Mock Test
  • Docs
  • ATSE
aglasem
  • CBSE
    • Date Sheet
    • Syllabus
    • Sample Papers
    • Question Papers
  • ICSE / ISC
  • State Boards
    • Date Sheet
    • Admit Card
    • Result
    • Sample Paper
    • Question Paper
  • NCERT
    • NCERT Books
    • NCERT Solutions
    • NCERT Exempler
    • Teaching Material
  • Mock Tests
  • Study Material
    • Notes
    • Solved Sample Papers
    • Maps
    • Writing Skill Format
  • Olympiads
    • ATSE
    • KVPY
    • NTSE
    • NMMS
  • School Admission
  • Entrance Exams
    • JEE Main
    • NEET
    • CLAT
  • Students Guide
    • Careers Opportunities
    • Courses & Career
    • Courses after 12th
  • Others
    • RD Sharma Solutions
    • HC Verma Solutions
    • Teaching Material
    • Classes Wise Resources
    • Videos
No Result
View All Result
aglasem
  • CBSE
    • Date Sheet
    • Syllabus
    • Sample Papers
    • Question Papers
  • ICSE / ISC
  • State Boards
    • Date Sheet
    • Admit Card
    • Result
    • Sample Paper
    • Question Paper
  • NCERT
    • NCERT Books
    • NCERT Solutions
    • NCERT Exempler
    • Teaching Material
  • Mock Tests
  • Study Material
    • Notes
    • Solved Sample Papers
    • Maps
    • Writing Skill Format
  • Olympiads
    • ATSE
    • KVPY
    • NTSE
    • NMMS
  • School Admission
  • Entrance Exams
    • JEE Main
    • NEET
    • CLAT
  • Students Guide
    • Careers Opportunities
    • Courses & Career
    • Courses after 12th
  • Others
    • RD Sharma Solutions
    • HC Verma Solutions
    • Teaching Material
    • Classes Wise Resources
    • Videos
No Result
View All Result
aglasem
No Result
View All Result

CBSE Class 12 Chemistry Notes: Periodic Properties – Periodicity in Atomic Radius and Ionic Radius

by Anand Meena
April 22, 2019
in 12th Class, Class Notes
Reading Time: 5 mins read
0
  • For normal elements

(a) In a period from left to right effective nuclear charge increases because the next electron fills in the same shell. So the atomic size decreases. For example the covalent radii of second period elements in Å are as follows –

Li Be B C N O F
1.23 0.89 0.80 0.77 0.74 0.74 0.72

(b)In a group, from top to bottom the number of shells increases. So the atomic size increases. Although the nuclear charge increases but its effect is negligible in comparison to the effect of increasing number of shells. For example the covalent radii of IA group elements in Å are as follows –

Li Na K Rb Cs
1.23 1.57 2.03 2.16 2.35
  • The atomic radius of inert gas (zero group) is shown largest in a period because of its Vander Waal’s radius which is generally larger than the covalent radius. The Vander Waal’s radius of inert gases also increases on moving from top to bottom in a group.
  • For transition elements – There are four series of transition elements

3d – Sc (21) to Zn (30)

4d – Y (39) to Cd (48)

5d – La (57), Hf (72) to Hg (80)

6d – Ac(89), Rf(104) …………. Unb (ununbium) 112 (incomplete)

(a) From left to right in a period

The atomic size first decreases due to the increase in effective nuclear charge and then becomes constant and then increases. In transition elements, electrons are filled in the (n-1)d orbitals. These (n-1)d electrons screen the ns electrons from the nucleus. So the force of attraction between the ns electrons and the nucleus decreases. This effect of (n-1)d electrons over ns electrons is called shielding effect or screening effect. The atomic size increases due to shielding effect and balances the decrease in size due to increase in nuclear charge to about 80%. Thus moving from left to right in a period, there is a very small decrease in size and it may be considered that size almost remains the same. In the first transition series the atomic size slightly decreases from Sc to Mn because effect of effective nuclear charge is stronger than the shielding effect. The atomic size from the Fe to Ni almost remains the same because both the effects balance each other. The atomic size from Cu to Zn slightly increases because shielding effect is more than the effective nuclear charge due to d10 structure of Cu and Zn. The atomic radii of the elements of 3d transition series are as under.

Sc Ti V Cr Mn Fe Co Ni Cu Zn
1.44 1.32 1.22 1.18 1.17 1.17 1.16 1.16 1.17 1.25

Inner transition elements – As we move along the lanthanide series, there is a decrease in atomic as well as ionic radius. The decrease in size is regular in ions but not so regular in atoms. This is called lanthanide contraction. The atomic radii in Å are as under

La Ce Pr Nd Pm Sm Eu Gd
1.88 1.82 1.83 1.82 – 1.80 2.04 1.80
Tb Dy Ho Er Yb Lu
1.78 1.77 1.76 1.75 1.94 1.73

There are two peaks one at Eu (63) and other at Yb (70). This is due to the difference in metallic bonding. Except Eu and Yb other lanthanides contribute three electrons in metallic bond formation. These two atoms contribute two electrons in the bond formation leaving behind half filled and completely filled 4f-orbitals respectively.

Cause of Lanthanide contraction – In lanthanides the additional electrons enters the (n-2)f orbital. The mutual shielding effect of (n-2) f electrons is very little because the shape of f-subshell is very much diffused. Thus the effective nuclear charge increases then the mutual shielding effect of (n-2)f electrons. The outer electrons are attracted more by the nucleus. Consequently the atomic and ionic radii decreases from La (57) to Lu (71)

This type of contraction also occurs in actinides. The jump in contraction between the consecutive elements in the actinides is greater than lanthanides. This is due to the lesser shielding of 5f-electrons which are therefore pulled more strongly by the nucleus.

(b) In a group

The atomic radius of elements increases moving from first transition series (3d) to second transition series (4d). This is due to the increase in number of shells with the increase in atomic number.

The atomic radii of second (4d) and third (5d) transition series in a group is almost same except Y(39) and La (57). In third transition series, there are fourteen lanthanides in between La (57) of III B and Hf (72) of IV B groups, so the atomic radius of Hf(72) decreases much due to lanthanide contraction in lanthanides. The difference in the nuclear charge in the elements of a group in first and second transition series is + 18 units while this difference in second and third transition series is + 32 units except Y (39) → La(57). Due to the increase of + 32 units in the nuclear charge there is a sizable decrease in the atomic radius which balances the increase in size due to the increase in number of shells.

So in a group moving from second to third transition series, the atomic radii of the elements almost remain the same except IIIB. The difference is about 0.02Å.
Chemistry CBSE Class 12 Notes/
Illustration 2. The radius of argon is greater than the radius of chlorine
Solution: In chlorine, the radius means the atomic or covalent radius which is actually half the intermolecular distance between 2 atoms whereas in Argon the radius means the Vander Waal’s radius as Argon is not a diatomic molecule. Vander Waal’s radius is actually half the distance between adjacent molecules. So Vander Waal’s radius being larger than atomic radius, Argon has got a larger radius than chlorine
Chemistry CBSE Class 12 Notes/

« Click Here for Previous Topic Click Here for Next Topic »

Click Here to Go Back to CBSE Class 12 Chemistry “Periodic Properties” All Topic Notes

Click Here for CBSE Class 12 Chemistry All Chapters Notes

To get fastest exam alerts and government job alerts in India, join our Telegram channel.

Tags: CBSE NotesClass 12 NotesClass 12th

Anand Meena

Full time entrepreneur, likes to indulge in writing reviews about the latest technologies apart from helping students in career and exam related topics.

Related Posts

CBSE 12 Answer Key 2022 for Term 2
12th Class

CBSE Class 12 Answer Key 2022 for Term 2

ISC Class 12 Answer Key
12th Class

ISC Physics Answer Key 2022 Class 12 Sem 2 (Out) – Check Solved Paper

ISC Class 12 Answer Key
12th Class

ISC Chemistry Answer Key 2022 Class 12 Sem 2 (Out) – Check Solved Paper

CBSE Class 12 Answer Key
12th Class

Class 12 English Core Answer Key / Solution for Term 2 CBSE Board Exam 2022 (Code 301) – Download PDF

Next Post
Class 11 Chemistry Notes General Organic Chemistry - AglaSem

Class 11 Chemistry Notes GOC - Intermediates of Organic Compounds

Discussion about this post

Registration Open!!

  • Panipat Institute Admission Open 2022
  • LPU Admission 2022 Open - India's Top Ranked University
  • AEEE 2020 - Amrita Vishwa Vidyapeetham
  • REVA University Admission 2022 Open

Term 2 Solved Sample Paper 2022

  • Class 8 Sample Paper Term 2
  • Class 9 Sample Paper Term 2
  • Class 10 Sample Paper Term 2
  • Class 11 Sample Paper Term 2
  • Class 12 Sample Paper Term 2

CBSE Board Quick Links

  • CBSE Date Sheet
  • CBSE Result
  • CBSE Syllabus
  • CBSE Sample Papers
  • CBSE Question Papers
  • CBSE Notes
  • CBSE Practice Papers
  • CBSE Mock Tests

Class Wise Study Material

  • Class 1
  • Class 2
  • Class 3
  • Class 4
  • Class 5
  • Class 6
  • Class 7
  • Class 8
  • Class 9
  • Class 10
  • Class 11
  • Class 12

For 2022

  • Solved Sample Papers
  • Maps
  • Revision Notes
  • CBSE
  • State Board

Study Material

  • Class Notes
  • NCERT Solutions
  • NCERT Books
  • HC Verma Solutions
  • Courses After Class 12th

Exam Zone

  • JEE Main 2022
  • NEET 2022
  • CLAT 2022
  • Fashion & Design
  • Latest
  • Disclaimer
  • Terms of Use
  • Privacy Policy
  • Contact

© 2019 aglasem.com

No Result
View All Result
  • CBSE
  • ICSE / ISC
  • State Board
  • NCERT
  • Mock Test
  • Study Material
  • Olympiads
  • Schools Admission
  • Entrance Exams
  • Student Guide
  • HC Verma Solutions
  • Videos

© 2019 aglasem.com

VIEEE 2022 Application Form Apply Now!!