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 hydration energy>Lattice energy.
- 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, LiCl with smaller Li+ion is more covalent than KCl.
b) Size of Anion:
-Bigger the anion, larger is its polarizing ability.
-The covalent character of Lithium halides is:
LiI>LiBr>LiCl>LiF
c) Charge of the ion:
-Covalent character increases with increase in charge.
-Covalent Characters is in order:
Na+Cl−<Mg++Cl2−<Al3+Cl3−
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.
-CuCl is more covalent than NaCl
e) If the electronegativity difference ≥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+δCl−δ, O−δ−H+δ, H−H, Cl−Cl etc.
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 →.
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. SO2; H3O+; H2SO4; SO3; NH4+.
Note:
- NaOH,KOH,Na2CO3 has both ionic and covalent bond.
- CO2,NH3.BF3,[Co(NH3)3Cl3] has covalent and co-ordinate bond.
- NH4Cl,CuSO4,K4[Fe(CN)6],[Cu(NH3)4]SO4,H2SO4,(NH)4SO4contains all three types of bond. i.e. Ionic, Covalent and Co-ordinate covalent bond.
- CuSO4.5H2O has ionic, covalent, coordinate and hydrogen bond also.
Hybridization:
- Mixing of two or more than two atomic orbitals.
- Rule:
x=21×[No. of valence electron of central atom (a) + No. of monovalent peripheral atom (b) − charge on cation (c) + charge of anion (d)]
If x=2 :
-sp−hybridized
-Shape: Linear geometry.
-Bond angle: 180∘
If x=3:
-sp2−hydridized
-Shape: Triangular geometry
-Bond angle: 120∘
If x=4:
-sp3−hybridized
-Shape: Tetrahedral
-Bond angle: 109∘
If x=5:
-sp3d−hybridized
-Shape: Bypyramidal
-Bond angle: 90∘ & 120∘
If x=6:
-sp3d2−hybridized
-Shape: octahedral
-Bond angle: 90∘
If x=6:
-sp3d3−hybridized
-Shape: Pentagonal bypyramidal
-Bond angle: 90∘ & 72∘
E.g. PCl5; x=1/2 (5+5)=5→ sp3d
CO3−;x=1/2 (4+0+2)=3→sp2
- 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, sp3−hybridized.
If no. of σ−bond=3, sp2−hybridized.
If no. of σ−bond=2, sp−hybridized.
Note:
-In Aniline and Phenol, N and O atom is sp2 -hybridized since lone pair of electron is involved in resonance.
-Structure of CO2 molecule is linear.
-Hybridization of C−C in benzene is sp2 hybridized.
-In Diamond, C-atom is sp3-hybridized while in graphite, C atom is sp2 hybridized.
-Bond angle of H2O is less then 109∘ 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 [Fe(CN)6]4−, the Fe atom is sp3d2 hybridized.