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:
1 POLARITYA 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).
2 d 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
3 Polarity 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.
4 Net 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
6 5. 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
7 6. 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
9 Induced 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.