CLASS :- 11
Atomic radius
Atomic radius means the distance from the centre of the nucleus to the electrons of outermost
shell are valency shell
the size of the atom very small 1.2 X 10 - 10 m
according to atomic orbital concept the probability of finding electrons is never zero even at
large distance from the nucleus
generally isolated atom not find out in our nature It exist in the form of
homo atomic or hetero atomic molecules form Then the size of atom also changed from one
state to another
As H-H , H-Cl , H-O-H
in covalent molecules Internuclear distance two time (twice) from the radius of an atom that
is now as covalent radius
Covalent radius
one half of the distance between the nuclei of two covalently bonded atom of the same
element in molecules
Homoatomic nuclear molecules
Internuclear distance Between two bonded atom
covalent radius = ……………………………………………………….
2
internuclear distance between two hydrogen atom in hydrogen molecules 74 pm
then atomic radius of hydrogen 37 pm
internuclear distance two chlorine atom in chlorine molecules 198 pm then
covalent radius of chlorine 99 pm
Covalent radius for heteronuclear molecules define as
In the heteronuclear molecules the distance between the centre of nucleus of the Two bonded
an atom and the mean position of the shared pair of electron between the bonded atoms
H-Cl heteroatomic molecules
Metallic radius
in metallic lattice of metal the metallic atom closely packed and held together why metallic Bond
one half of the internuclear distance between the the two metallic Bond bonded neighbouring
atoms of a metal in a metallic lattice
Example Internuclear distance between two atom in copper metallic lattice 256 pm therefore radius
metallic of copper 128 pm
However l you are always remember that atomic or metallic radius, shorter than the atomic radii of
atom in the uncombined form
Van Der waals radius
In the solid state One half of the internuclear distance between the nuclei of two adjacent atom of the
molecular substance belonging to the two neighbouring molecules
The internet distance between two adjacent chlorine atom in the solid state 360 pm therefore
Van Der waals radius but 180 pm
the covalent radius of chlorine 99 pm and Wonderwall radius 180 pm it means Van Der waals
radius always greater than covalent radius
Ionic radius
The ions for ejection of electron and acquire positive charge are called Cations while ion form by accept
of electron get negative charge are called a Anions
the effective distance from the centre of the nucleus of the ion up to which it has an influence in the
ionic bond
in ionic compound
internuclear distance = radius of cations + radius of anion
example the inter nucleoid distance of sodium chloride 276 pm which corresponding to the sum of
the ionic radii of sodium and chloride ions
(1)The radius of positive ions that time is always is smaller than that of the parent atom
The sodium cations Ionic radius 95 pm and sodium atom atomic radii 186 pm it means When sodium atom loss of one electrons and change into sodium cations then outer third
shell of sodium atom disappear in sodium ions this is the cause why sodium cation smile size compare
to sodium atom
Na → Na+ + e-
1s2,2s2,2p6,3s1 1s2,2s2,2p6,
186 pm 95 pm
(2)The Negative Ion is always larger than that of the corresponding atom
the Negative Ion is form When atom accept one or more Electron
an Chlorine atom accept of one electron and form chloride ion
The Chloride ion radius 181 pm but chlorine atomic radius 99 pm
Cl + e- → Cl- 1s2,2s2,2p6,3s2,3p5 1s2,2s2,2p6,3s2,3p6
99 pm 181pm
the Ionic radius of chlorine more than to chlorine atoms because when new electrons enter in
their respected outer cell the inter electronic repulsion between electron - electrons increases
and electrons disperse enlarge volume And also effective nuclear charge per an electron is
reduced and the electrons cloud is held less tightly by the nucleus.
Verizon of atomic and ionic radii in the periodic table
variation in a period
the atomic radius on moving left to right in period gradually decrease because
interaction between effective nuclear charge and electron increase
The atomic radius in period continuously decrease
But oxygen atomic radius more than to nitrogen because in case of oxygen(1s2,2s2,2px2py1pz1) the outer 2p subshell electronic configuration is responsible for electronic repulsion
between electron and electron , electrons disperse enlarge volume because last
electrons paired of 2P subshell electron and in nitrogen(1s2,2s2,2px1py1pz1) 2P subshell filled in unpaired form and electronic repulsion
minimum
Variation in a group
On moving up to bottom in a group atomic radius are Ionic radius gradually increase because
always Valence Electrons enter new energy level
