Hi fellows ,
this is Chemaddicts to the solution!!!!
Today we are going
to discuss about the Covalent and ionic
character.
So let’s get
started !!
We will come to know
about the following concepts :
1) Covalent
character
2) Ionic
character
3) The
relationship between ionic and covalent character.
1) Covalent character :
What is a
covalent character ?
A covalent
character is the covalency in ionic compounds which is due to the
High Polarising power of Cations and High
Polarisability of anions.
Diagram :
Then gradually,
 |
| Finally the oxide ion is being distorted by Magnesium ion... |
High Polarising power of Cations :
- It is the ability of a cation to distort the electron cloud of the anion in an ionic compound.
- Higher polarising power of cations means that ionic compound gains more covalent character.
Polarising power of cation depends on :
1) Size of Cations .
2) Charge of Cations . ( Not the Nuclear charge )
Diagram :
 |
| Here charge of the ions are involved here , not the nuclear charge. |
1) Size of Cations :
- Decreasing size of cations results in greater polarising power. From here, we can deduce that :
Here charge of cations are same (constant).
Therefore, small cations can distort the electron cloud
of anions more effectively.
2) Charge of Cations:
- Increasing Charge on Cations ( Not the nuclear charge ) results in increasing the Polarising power of Cations.
- Greater Charge on Cations means it can have more attraction with the electron cloud of anions.
A new
relationship can be obtained between Polarising power and the following
factors :
1) Size of
Cations
2) Charge of Cations
Now we are combining
the equations that we have derived before,
Where,
ratio is
also known as the charge density.Charge Density:
It is simply a ratio
of charge and size.
Polarising power cations down the Group:
Polarising power of cations decreases
down the group.
Let’s see how,
LiCl * Charge
on the cations remain same.
NaCl * Size
of Cations increases .
KCl * Charge density of cations decreases.
RbCl * So, the anions are distorted less.
CsCl *
Covalent Character decreases
* Ionic
Character increases
Down the Group 2 ionic compounds ,
BeO * Charge
on the cations remain same.
MgO * Size of Cations increases .
CaO *
Charge density of cations decreases.
SrO *
So, the anions are distorted less.
BaO *
Covalent Character decreases
* Ionic Character increases
High
Polarisability of anions :
High polarisibility of anions is
the ease of distortion of the electron cloud of an anion
or
the ease with
which Anions responds to the polarising power of the cations.
Diagram:
 |
| Cations are able to distort the electron cloud of anions because there is a weaker attraction between outer electron shells and nucleus of anions. |
Polarisibility
of anions depends on size :
Polarisibility
of anions increases with increasing size.
Down
the Group7 ionic compounds ,
LiF * Charge
on the Anions remain same.
LiCl * Size of Anions increases .
LiBr *
Polarisibility of Anions increases.
LiI * So, the
anions are distorted more .
* Covalent
Character increases
*
Ionic Character decreases
Ionic character :
Ionic character
is the opposite of covalent character.
Cations with
greater size will have higher ionic character.
Anions with smaller
size will have higher ionic character.
This is because
of cations cannot distort the electron cloud.
When electron
distortion becomes weaker or impossible, then that compound would have high
ionic character and low covalent character.
Down the Group 1
ionic compounds ,
LiCl * Charge
on the cations remain same.
NaCl * Size of Cations increases .
KCl * Charge density of
cations decreases.
RbCl * So, the
anions are less distorted.
CsCl *
Covalent Character decreases
* Ionic
Character increases
Down the Group 2 ionic compounds ,
BeO * Charge
on the cations remain same.
MgO * Size of Cations increases .
CaO *
Charge density of cations decreases.
SrO * So,
the anions are less distorted .
BaO *
Covalent Character decreases
* Ionic Character increases
Down the Group7 ionic compounds ,
LiF * Charge
on the Anions remain same.
LiCl * Size of Anions increases .
LiBr *
Polarisibility of Anions increases.
LiI * So, the
anions are distorted more .
* Covalent
Character increases
* Ionic Character decreases .
Well, this is the end of today's post ! Follow me on this blog for getting updated with my posts like this. And you may get a video solution to a problem on this topic by the clicking the following link :
See you in the next post!! Bye Bye!!!
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