NEET Exam  >  NEET Notes  >  Chemistry Class 11  >  Quick Revision: Classification of Elements & Periodicity in Properties

Quick Revision: Classification of Elements & Periodicity in Properties | Chemistry Class 11 - NEET PDF Download

Download, print and study this document offline
Please wait while the PDF view is loading
 Page 1


PERIODIC TRENDS IN PROPERTIES
A. Atomic Size (or atomic radius)
Atomic radius is the size of the atom of an element. Atomic radius is defined as “the distance from the centre
of the nucleus upto the centre of outermost electron.” It is measured in Angstrom unit (Å). It is not possible
to measure exact atomic radius as an atom is unstable and it cannot be isolated to get its radius. Moreover,
the exact position of the outermost electron is uncertain. The values for radii are obtained from X-ray
measurements. Following points are to be noted in this context :
(a) The size of an atom or ion decreases in a horizontal period as we move from left to right.
(b) The atomic radius increases in a group with the rise in atomic number.
(c) A positive ion (cation) is smaller than the corresponding atom : A positive ion or cation is formed
by the loss of one or more electrons from an atom and the number of protons remains the same in the
nucleus. Thus the ratio of the positive charge in the nucleus to the number of electrons i.e., effective nuclear
charge increases. Hence the force of attraction of nucleus to the outer electrons increases thus decreasing
the size of cation. In case of alkali metals, the removal of an electron removes the entire outermost shell.
(d) A negative ion (anion) is bigger than the corresponding atom : In the formation of negative ion (anion)
one or more electrons(s) are added to the atom. This results in the expansion of the size of the nuclear
charge, which in turn decreases the force of attraction and increases the size of an anion or the pull
exercised by the nucleus on the electron becomes less i.e., they move a little farther resulting in an
increase in the ionic size.
Note : Size of Iso-electronic ions : These are such cations or anions which carry the same number
of electrons. The size of such ions depends upon the effective nuclear charge. Greater the
nuclear charge of an ion, greater will be the force of attraction for same number of electrons.
As a result, the size of the ion decreases. For example :
N
3–
, O
2–
, F
–
, Na
+
, Mg
2+
 and Al
3+
 are isoelectronic ions, among these N
3–
 is largest (1.71 A) and
Al
3+
 is smallest (0.50 A).
B. Ionization Enthalpy
It is the amount of energy required to remove most loosely held electron from the ground state of an Avogadro
number of the isolated atoms, ions or molecules in the gaseous state. The ion formed by loss of first electron
may lose further electrons and thus we may have successive ionization energies for removal of 2nd, 3rd and
4th electrons in the gaseous state.
Ionization is always an endothermic process and ionization energies are therefore always assigned positive
values.
Read More
172 videos|306 docs|152 tests

Up next

FAQs on Quick Revision: Classification of Elements & Periodicity in Properties - Chemistry Class 11 - NEET

1. What is the periodic table and how is it organized?
Ans. The periodic table is a tabular arrangement of chemical elements, organized based on their atomic number, electron configuration, and recurring chemical properties. It is divided into periods (rows) and groups (columns), with elements in the same group having similar properties.
2. What are the main groups in the periodic table and what are their properties?
Ans. The main groups in the periodic table are Group 1 (Alkali metals), Group 2 (Alkaline earth metals), Group 13 (Boron group), Group 14 (Carbon group), Group 15 (Nitrogen group), Group 16 (Chalcogens), Group 17 (Halogens), and Group 18 (Noble gases). Each group has distinct properties, such as alkali metals being highly reactive and noble gases being inert.
3. How are elements classified in the periodic table?
Ans. Elements in the periodic table are classified based on their electronic configuration and chemical properties. They are organized into groups, where elements within the same group have similar properties due to their similar outer electron configurations.
4. What is periodicity in properties of elements?
Ans. Periodicity in properties of elements refers to the recurring pattern of their properties in the periodic table. Elements in the same period show a gradual change in properties as the atomic number increases. For example, atomic radius generally decreases across a period, while ionization energy increases.
5. What are the trends in atomic size and ionization energy across a period?
Ans. Across a period in the periodic table, atomic size generally decreases from left to right due to an increase in effective nuclear charge. Ionization energy, on the other hand, generally increases from left to right as it becomes more difficult to remove an electron from a smaller atom with a stronger attraction between the nucleus and electrons.
172 videos|306 docs|152 tests
Download as PDF

Up next

Explore Courses for NEET exam
Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Related Searches

Free

,

Objective type Questions

,

MCQs

,

Extra Questions

,

Previous Year Questions with Solutions

,

past year papers

,

Viva Questions

,

Important questions

,

practice quizzes

,

Semester Notes

,

Summary

,

study material

,

Exam

,

Sample Paper

,

Quick Revision: Classification of Elements & Periodicity in Properties | Chemistry Class 11 - NEET

,

pdf

,

Quick Revision: Classification of Elements & Periodicity in Properties | Chemistry Class 11 - NEET

,

Quick Revision: Classification of Elements & Periodicity in Properties | Chemistry Class 11 - NEET

,

mock tests for examination

,

ppt

,

video lectures

,

shortcuts and tricks

;