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Physical Chemistry

Language of Chemistry Stoichiometry Atomic Structure Oxidation and Reduction Periodic Table Acid and Base Electronic Theory of Valency Equivalent Weight and Atomic Weight

Physical Chemistry-II

Non-Metals

Inorganic Chemistry

Electronic Theory of Valency

Octet Rule:

Elements with each electrons in their valence shell ( state of octet) are said to be most stable form of electronic configuration and such elements do not take part in bond formation.
Inert gas elements (except $He$ , which is duplet) passes such stable electronic configuration.
Element attain octet state either by the transfer, sharing or coordinate of valence electrons.

Electro valency (Electrovalent/Ionic bond):

Formation of bond is exothermic process (i.e. energy releases).
The bond formation by the complete transfer of electron from valence shell is called electrovalent bond.
Electro valency is the number of electrons gained or lost.

Characteristics of Ionic Bond:

They generally have high melting and boiling point.
They are highly soluble in solvents with high dielectric constant but insoluble in non-polar solvent like benzene, ether, etc. The ions dissolve in water if $h y d r a t i o n e n er g y > L a tt i ce e n er g y$ .
They do not conduct electricity in solid state but conducts electricity in molten or solution state.
Favourable condition for formation of ionic bonds are low charge in ions, large cation and small anion.

Note:

-No bond is $100%$ ionic, it has same $%$ of covalent character which is given on the basis of Fajan's rule:

Fajan's Rule:

a) Size of cation:

-Smaller is the cation, greater is its polarizing power.

-Thus, $L i Cl$ with smaller $L i^{+}$ ion is more covalent than $K Cl$ .

b) Size of Anion:

-Bigger the anion, larger is its polarizing ability.

-The covalent character of Lithium halides is:

$L i I > L i B r > L i Cl > L i F$

c) Charge of the ion:

-Covalent character increases with increase in charge.

-Covalent Characters is in order:

$N a^{+} C l^{-} < M g^{++} C l_{2}^{-} < A l^{3 +} C l_{3}^{-}$

d) Electronic Configuration:

-When two cation have same charge and size, the one having $18$ electrons in outermost shell will have larger polarizing power than a caution having $8$ electrons in outermost shell.

- $C u Cl$ is more covalent than $N a Cl$

e) If the electronegativity difference $\geq 1.8$ between combining molecules then the bond formed will be ionic.

Covalency (Covalent Bond):

Bond formed by the mutual sharing of valence electrons.
If difference of electronegativity $(△ E)$ , $0.4 < △ E < 1.8$ , the bond will be polar-covalent.
If difference of electronegativity $(△ E)$ , $0 - 0.4$ , the bond will be non-polar covalent.
E.g. $H^{+ δ} C l^{- δ}$ $, O^{- δ} - H^{+ δ}, H - H, Cl - Cl e t c$ .

Characteristics of Covalent Bond:

These compound are molecular in nature.
They are insoluble in water and soluble in non-polar solvents like benzene.
It is a weaker bond. So, they have low melting and boiling point.
Unlike ionic compound, covalent compound can show structural and space isomerism.

Co-ordinate Covalent or Dative Bond:

Special type of covalent bond, which is formed by one sided sharing of lone pair of electrons.
The atom that donates a pair of electron is called donor and atom which accepts the electron pair is called acceptor.
It is represented by $\to$ .

Characteristics of Co-ordinate Covalent Bond:

They exists in all three states .i.e. solid, liquid and gas.
They show isomerism and stero-isomerism.
They are poor conductor of electricity.
Their melting points and boiling points are greater than covalent compounds and less than ionic compounds. E.g. $S O_{2}; H_{3} O^{+}; H_{2} S O_{4}; S O_{3}; N H_{4}^{+}$ .

Note:

$N a O H, K O H, N a_{2} C O_{3}$ has both ionic and covalent bond.
$C O_{2}, N H_{3} . B F_{3}, [C o (N H_{3}) 3 C l_{3}]$ has covalent and co-ordinate bond.
$N H_{4} Cl, C u S O_{4}, K_{4} [F e (CN) 6], [C u (N H 3) 4] S O_{4}, H_{2} S O_{4}, (N H) 4 S O_{4}$ contains all three types of bond. i.e. Ionic, Covalent and Co-ordinate covalent bond.
$C u S O_{4} .5 H_{2} O$ has ionic, covalent, coordinate and hydrogen bond also.

Hybridization:

Mixing of two or more than two atomic orbitals.
Rule:

$x = \frac{1}{2} \times [N o . o f v a l e n ce e l ec t ro n o f ce n t r a l a t o m (a) + N o . o f m o n o v a l e n t p er i p h er a l a t o m (b) - c ha r g e o n c a t i o n (c) + c ha r g e o f ani o n (d)]$

If $x = 2$ :

- $s p - h y b r i d i ze d$

-Shape: Linear geometry.

-Bond angle: $18 0^{\circ}$

If $x = 3$ :

- $s p^{2} - h y d r i d i ze d$

-Shape: Triangular geometry

-Bond angle: $12 0^{\circ}$

If $x = 4$ :

- $s p^{3} - h y b r i d i ze d$

-Shape: Tetrahedral

-Bond angle: $10 9^{\circ}$

If $x = 5$ :

- $s p^{3} d - h y b r i d i ze d$

-Shape: Bypyramidal

-Bond angle: $9 0^{\circ} & 12 0^{\circ}$

If $x = 6$ :

- $s p^{3} d^{2} - h y b r i d i ze d$

-Shape: octahedral

-Bond angle: $9 0^{\circ}$

If $x = 6$ :

- $s p^{3} d^{3} - h y b r i d i ze d$

-Shape: Pentagonal bypyramidal

-Bond angle: $9 0^{\circ} & 7 2^{\circ}$

E.g. $PC l_{5}; x = 1/2 (5 + 5) = 5 \to s p^{3} d$

$C O_{3}^{-}; x = 1/2 (4 + 0 + 2) = 3 \to s p^{2}$

The hybridization can also predicted by formation of $π$ and $σ$ bond.
$σ$ -bond is strong bond. During formation of atom, lone pair is converted as $σ -$ bond.

-If no. of $σ -$ bond= $4$ , $s p^{3} -$ hybridized.

If no. of $σ -$ bond= $3$ , $s p^{2} -$ hybridized.

If no. of $σ -$ bond= $2$ , $s p -$ hybridized.

Note:

-In Aniline and Phenol, N and O atom is $s p^{2}$ -hybridized since lone pair of electron is involved in resonance.

-Structure of $C O_{2}$ molecule is linear.

-Hybridization of $C - C$ in benzene is $s p^{2}$ hybridized.

-In Diamond, $C$ -atom is $s p^{3}$ -hybridized while in graphite, $C$ atom is $s p^{2}$ hybridized.

-Bond angle of $H_{2} O$ is less then $10 9^{\circ}$ due to presence of lone pair of electron on oxygen.

- $π$ -bond are only formed only when $σ$ -bond is already formed.

- Sigma bond is formed by head on overlapping and $π$ -bond is formed by lateral or sideways overlapping.

-In $[F e (CN)_{6}]^{4 -}$ , the $F e$ atom is $s p^{3} d^{2}$ hybridized.