TlCl more stable thanTlCl3

Why is TlCl more stable than TlCl₃ molecule?

‘Tl’ is a group 13^th or p-block heavier element. The outer electronic configuration of thallium is, [Xe] 4f¹⁴ 5d¹⁰ 6s²6p¹.

From the electronic arrangement of Tl, it has been found that, the valence electron of thallium element is 3.

So, the oxidation state of Tl should be +3 . But it has been found that , +3 oxidation state of Tl is less stable than +1 state.

Inert pair effect-definition-examples-cause-and consequences

·        Inert pair effect definition in chemistry

Inert pair effect is generally exhibited by the P-block elements. There are some 

heavier P-block elements,[ Such as, Sn, Pb, Sb, Bi etc ] with molecular formula ns2 np1-6 , have a less tendency to leave their outer most S-electrons easily.

That is, the electron present in the outer most S-orbital , does not participate in the formation of a chemical bond.

The tendency of this electron pair to stayed inert, is called inert pair effect.

Covalent bond-polar covalent bond-non polar covalent bond-examples

·        What is polar covalent bond ?

If a covalent bond is formed by sharing of electron between two dissimilar or different atoms, then this covalent bond is called polar covalent bond.

Because, in this case one atom between the two is more electronegative than the other one.

Now, more electronegative atom have a tendency to attract the bonded electron pair towards itself.

As a result, the shared electron partially moved towards the more electronegative atom.

Due to this unsymmetrical charge distribution, more electronegative element gets partial negative charge and the less electronegative element gets partial positive charge.

In this way, the covalent bond change into polar covalent bond and the molecule becomes polar molecule.

For example, Hᵟ⁺ – Fᵟ^- , Hᵟ⁺ – Clᵟ^- , Hᵟ⁺– Brᵟ^- etc molecules contain polar covalent bond.

The polar covalent bond is, therefore, has partial ionic character .

The two opposites charges at the ends are called electrical poles and the molecules are called dipolar molecules.

·        What is non polar covalent bond ?

Covalent bond is formed by sharing of electron between two similar or dissimilar atoms. 

There are two types of covalent bond, namely, non polar covalent bond and polar covalent bond.

The covalent bond is formed by sharing of electron between two identical or similar atoms, is said to be non polar covalent bond.

In this type of covalent bonding, the shared electron pair is attracted equally by both the atoms and lies exactly midway between them.

The resulting covalent compound is called non polar molecule.

For example, hydrogen , chlorine , bromine, oxygen, nitrogen etc molecule contain non polar covalent bond.

·        What is polar and non polar molecules ?

If a covalent bond is formed by sharing of electron between two identical or 

similar atoms, then the covalent bond is said to be non polar covalent bond and the resulting covalent compound is called non polar molecule.

For example, hydrogen , chlorine , bromine, oxygen, nitrogen etc molecule contain non polar covalent bond.

On the other hand, if a covalent bond is formed by sharing of electron between 

two dissimilar or different atoms, then this covalent bond is called polar covalent bond and the resulting covalent compound is called polar molecule.

In this type of molecule, the polarity arises due to difference in electro-negativity of the two dissimilar atoms.

Octet rule-definition-limitations of octet rule-hypovalent-hypervalent compounds

Octet rule-definition in covalent molecules .

 Mostof the elements [ except H, Li , B etc ] have a tendency to attain eight electrons in their outer most valence shell through loss or gain of electrons or by 

sharing of electrons at the time of chemical reaction, so that they can attain the next inert configuration.  

This tendency of elements to maintain eight electrons in their own valence shell, is called octet rule.

Polarization meaning-Ionic potential-polarizability and polarizing power

Polarization meaning in chemistry

Polarization in chemistry means deformation of symmetric electron charge cloud of anion by cation.

In case of ionic crystal , it has been observed that, the positive electric field of cation pull the electronic sphere of an anion from their equal distance.

But the positive electric field of cation repulse the nucleus of anion. As a result, the deformation of symmetric electron charge cloud of anion by cation is called polarization of anion. 

Fajan’s rule-definition-postulates and examples

Fajan’s rule definition in chemistry 

It is a common experience that many times an ionic bond has some covalent character and a covalent bond has some ionic character.

Fajan’s rule is related to the covalent character in ionic bond or ionic compounds.

It has been experimentally observed that a polar covalent bond is more stable than a pure covalent or a pure ionic bond .

The higher the degree of ionic polarization , the greater is the stability of the polar covalent bond .

Markownikoff’s-rule-definition-peroxide effect-limitation

Markownikoff’s  rule in chemistry  

When an addendum (halogen acids) is added to an asymmetric alkene, the negative part of the addendum is added on that double bonded carbon atom that contains least number of hydrogen atom.This statement is known as Markownikoff’s  rule.

For example, addition of HBr to prop-1-ene gives 2-bromo propane.

VSEPR theory-definition-postulates-shape and limitations

VSEPR  theory and shape of covalent molecules 

The geometry of covalent molecules depends upon the number and arrangement of electron pairs [which present in the valence shell of the central atom], due to electrostatic repulsion between bond pair and lone pair of electrons.

Lanthanide contraction-definition-causes-consequences in chemistry

Lanthanide contraction definition in chemistry

In case of lanthanide elements , it has been experimentally found that with increasing atomic number , the atomic and ionic size of lanthanide elements gradually decreases from lanthanum to lutetium.

It is very much regular for lanthanide ions ( Ln ³⁺) . It will be seen that on going from  La 3+ to Lu 3+, the ionic radius shrinks from 115 pm to 93 pm .

The  steady decrease in ionic radius all along the series amounting in all to 22 pm , is called lanthanide contraction .The lanthanide contraction is also known as 4f or f contraction .

Lanthanide  contraction  causes

In case of lanthanide series elements, the differentiating electron entered into the 4f-orbital one at each step . 

Now, the shielding or screening effect of ‘f’-orbital is very much less than ‘s’ , ‘p’ even than that of ‘d’-orbital . This is due to the shape of ‘f’-orbital.

Hence the effective nuclear charge increases by one at each step . Consequently , the inward pull experienced by the 4f electrons increases.

As a result , the size of the entire 4f ⁿ shell reduces . The sum of the successive reductions  gives the lanthanide contraction .

Lanthanide contraction consequences

( I ) Change of basic properties of lanthanide metal hydroxide compounds .

Due to lanthanide contraction , the ionic size from La 3+ to Lu 3+ along lanthanide series gradually decreases.

As a result, the covalent properties of lanthanide metal hydroxide compounds  regularly increases [according to Fajan’s rule,]from lanthanum to lutetium .

That is ,Lu ( OH )₃ is more covalent than La ( OH )₃ . Now , with increasing covalent character, their basic property decreases .