Presentation on theme: "POLARITY A polar bond has separate centers of positive and negative charge. A molecule with separate centers of positive and negative charge is a polar."— Presentation transcript:
1POLARITYA polar bond has separate centers of positive and negative charge. A molecule with separate centers of positive and negative charge is a polar molecule.The dipole moment (m) of a molecule is the product of the magnitude of the charge (d) and the distance (d) that separates the centers of positive and negative charge.m = ddA unit of dipole moment is the debye (D).
2d is the separation distance of the charge Depending on the Electronegativity of atoms A & B in an AB molecule , it is possible to predict whether A-B bond in polar or non-polar covalent bond or an ionic bond.a) (XA-xB)=0 - Non-polar covalent bond, Molecule is homonuclear A-A or B-B .b) (xB – xA) = relatively small – e.g. O-H, Cl-H Bond is covalent with some ionic character/polarity (Polarity – separation of charges) Polar covalent bond.c) (xB – xA) = Very large – complete transfer of electron; the bond is ionic, A+-B -Unitsif l = 1 A0 µ = x e.s.u.µ = x in CGS units= e.s.u. cm = 1 D Debye)The dipole moment, m, is given by= Qd where Q is the charge andd is the separation distance of the charge
3Polarity and shapeThe shape of the molecule directly influences the overall polarity of the molecule.By knowing the polarity the shape of molecule can be ascertained.Homonuclear Diatomic mol- AAD.M. = 0Molecule has symmetrical dumbbell shape2. Heteronuclear diatomic mol – AB.Some value of D.M. but still are symmetrical dumbbell shape.
4Net dipole 3. Triatomic molecule a) D.M. =0 symmetrical and linear Example – 1. BeCl22. CO2 has polar bonds, but is a linear molecule; D.M. of C-O is 2.3 D, the bond dipoles cancel each other and it has no net dipole moment (m = 0 D). Bonds are polar but molecule, is non-polarb) D.M. >0unsymmetrical shape e.g. H2 OTwo O-H bonds, as there is some D.M. so the mol is angular The H─O bond is polar. Both sets of bonding electrons are pulled toward the O end of the molecule. The net result is a polar molecule. The bond dipoles do not cancel (m = 1.84 D), so water is a polar molecule.Net dipole
65. Penta-atomic molecule D.M.=0Symmetrical tetrahedral – all four groups samee.g. symmetrical PtCl4Methaneb) D.M.>0unsymmetrical, Tetrahedral but with D.M. e.g. CH3 Clall 4 bonds are not identical in polarity3 C-H & 1 C-Cl, So values are not cancelled
76. Hexa atomic molecule –a) D.M. = 0Symmetrical arrangement of bonds. PCl 5 is non polar. All the bonds cancel out each other. There are no net dipole.b) D.M.>0Different atomse.g.7. Hepta atomic molecule –D.M. = 0Symmetrical octahedra
9Induced dipole momentUnder the inference of electric field a non-polar molecule shows some charge separation. As the electron cloud is mobile it gets polarized. This induced polarity is temporary and is given asµi =αE where E- Electric field and α- Molar polarisabilityThe polarisability of molecule increases with size of ion e.g. I- is more polarisable than Cl- ion.