1. CLASSIFICATION OF ELEMENTS & PERIODICITYIN PROPERTIES
BY :- VIVEK KUMAR
:- BS-MS ( 1ST YEAR)
:- SCHOOL OF BASIC SCIENCES & RESEARCHES

2. Content
 Mendeleev’s Periodic Table
 Modern’s Periodic Table
 Periodicity & Cause of Periodicty
 Atomic Radius
o Co-valent Radius
o Vander Wall’s Radius
o Metallic Radius
 Ionic Radius
o Cation
o Anion
 Ionization Enthalpy / Energy
 Electron Gain Enthalpy

3. ELECTRONEGATIVITY
VALENCY

4. Mendeleev’s Periodic Table
 Mendeleev’s arrange them known 63 elements in order of
their increasing atomic mass and observed regularity in
properties of elements .
 Among chemical properties mainly considered Oxides &
Hydrides
 Mendeleev’s Periodic Law
o “Physical & Chemical properties of elements are periodic
function of their atomic masses’’
Achievements
 More systematic and easy approached .
 Correction of atomic mass of few elements on the basis of
position of elements in periodic table Mendeleev corrected
atomic masses of few elements.

5.  Production of few elements
Predicted eka-Boron eka-Aluminium eks-silicon
Later Scandium Gallium Germanium
Discovered
Limitations
o Position of hydrogen was not justified as it represents to both
alkali metals (1st group) (Li, Na, K….etc) & halogens (Cl , Br,
F).
o Position of Isotopes could not be justified as these are the
atoms of same elements having same atomic no. but
different atomic mass.
o Some of the elements with dissimilar properties where put together.
Eg:- Coinage metal like Cu,Ag & Au where arreanged with alkali metals .

6. o Mendeleev could be explain the cause of
periodicity.
o Nine elements in 8th group where arranged in the form of three
trends without any justification
o Their was no separate place for Lanthanides & Actinides
Modern Periodic table
 In 1913 “ Henry Moseley” showed that atomic no. is more
fundamental properties then atomic weight accordingly to
introduce.
Modern Periodic Law
 “Physical & Chemical properties are the periodic function of their no.” .
 Elements when arranged in order of increasing atomic no. led to the
classification called modern periodic table.
 Total 18th vertical column ------ GROUP
 7 Horizontal rows ------------Periods

7. Periodicity
Reaccurence of elements with similar properties
At regular interval when arranged in order of increasing
Atomic no. is called periodicity.
 Cause of periodicity
Similar electronic configuration in outermost shell at definite
interval.

9. Atomic Radius
 Generally it is defined as the distance of seperation b/w
centre of nucleus and outer most shell of electron in an
isolated atom.
 Difficulties In Measuring Atomic Radius
o According to probability picture of an atom there is no
definite boundary of atom.
o It is not possible to isolate an atom.
o Atomic radius of an atom varies from one bounded state to
another. Eg.:- Cl in Nacl & In Cl2.
Co-valent Radius
• It is defined as half of the distance of separation b/w nuclei
of two covalently bonded similar atom by a single covalent
bond.

10. Vander Wal’s Radius
 Half of the inter nuclear distance b/w adjacent atom (non-
bonded) in a compound in solid state.

11.  It is also known as inert gas radii because
radius of nobel gases is always measured in term of Rvw
Because they are generally not involved in bond formation.
(except Xe , Kr).
Metallic Radius
Half of the inter nuclear distance separating metal
cores in a metallic crystals.
General trends
o Across period L to R
( Atomic radius decreases due to increases in
effective nuclear charge which tends to pull electron
cloud closer.

12. o Down the group atomic radius increases due
To increases in no. of shells and decreases in effective
Nuclear charge.
 Shielding Effects
The inner electron screen the outer electron from nuclear
attraction.
Ionic Radius
It is defined as the distance from centre of nucleus
up to which it interfaces the ionic bond (e- cloud).
Cation
Cation is always smaller than parent atom ( due to decreases in no. of
electron nuclear attraction per electron increases)

13. Anion
Anion is greater than parent atom ( due to increases in no. of
electron per e- nuclear attraction decreases and hence e-
cloud moves furthers.
Ionization Enthalpy / Energy
The amount of energy required to remove an electron from
outer most shell of isolated gases atom . So as to convert it
into gases +ve ions.
Endothermic always +ve
Factors effecting Ionization Enthalpy
o Ionization Enthalpy is directly proportional to Nuclear charge
o Ionization Enthalpy is inversely proportional to size
o Ionization Enthalpy is inversely proportional to shielding
effect.

14. o Electronic Arrangement
o Half field and fully field orbital shows extra stability and hence
have higher Ionization Energy.
Successive Ionization Energy
Ionization Energy is always higher ( energy required to
remove subsequent electron.
Mg--Mg+Mg2+
IE1 IE2
Electron gain Enthalpy
The amount of energy released when an extra electron is
added to isolated neutral gases atom . So as to convert it in to
gases –ve ions .
Depending upon the process is exo or endothermic .
O+e-  O- + e-
( released energy) (provide energy)

15.  Higher the magnitude of electron gain
Enthalpy more is the tendency of an atom to gain an e-
and besides this it is also important to retain an e- . The
highest –ve values are Halogens .
Factors Effecting of Electron gain Enthalpy
Electron gain Enthalpy is inversely proportional to atomic
sizes .
Electron gain Enthalpy is directly proportional to Nuclear
charge.
Electronic Arrangement
Atoms of element having half field & fully field orbital have
very low magnitude of Electron gain Enthalpy.
Successive Electron gain Enthalpy
O + e-  O- (-ve) ( exothermic)
O- + e-  O2-(+ve) (endothermic)
Repulsion  overcome + energy is required

16. Electro negativity
The tendency of an atom to attract shared paired of
electron towards itself is called electro negativity.