POLARITY AND SOLUBILITY: “Like dissolves like”

Review of shapes: What are the five basic shapes?  Linear  Trigonal Planar  Tetrahedral  Trigonal Pyramidal  Bent

Review of Bonding: Ionic or covalent?  Ionic = metal + nonmetal  Covalent = nonmetal + nonmetal  Nonpolar Covalent = electrons shared equally  Polar Covalent = electrons shared unequally

Review of Electronegativity  Electronegativity is the ability of an atom to attract electrons in a compound.  The more electronegative element in a compound will pull the electrons towards itself.  The difference in electronegativity determines if the bond is nonpolar, polar or ionic.

Definitions of Polarity  Polar bond — bond involves unequal distribution of electrons  Polar Molecule - A molecule with a net dipole as a result of the opposing charges (i.e. having partial positive and partial negative charges) from polar bonds arranged asymmetrically molecule dipolepolarmolecule dipolepolar  Dipole—charges in a molecule are separated; use and

Electronegativity and Bond Type  Electronegativity difference determines the type of bond formed  Subtract the electronegativities of the elements in the bond.  If the difference is:  0.0 to 0.2 the bond is nonpolar covalent  0.3 to 1.4 the bond is polar covalent  > 1.5 the bond is ionic IF a metal is involved  HOWEVER If only nonmetals are involved, the bond is considered polar covalent.

Periodic Table of Electronegativities

Examples  Carbon Disulfide  Formula CS 2  Since the electronegativities of C and S are both 2.5, the difference will be 0 and you have a nonpolar bond.  Water  Formula H 2 0  EN H = 2.1  EN O = 3.5   EN =1.4 polar covalent

More Examples  Sodium bromide  formula = NaBr;  EN Na = 0.9,  EN Br = 2.8  has a ΔEN = 1.9 and ionic bond  Hydrogen fluoride  formula = HF;  EN H = 2.1,  EN F = 4.0  ΔEN = 1.9 and polar covalent bond

Polarity and Molecular Geometry  Draw Lewis Structure & Bar Diagram;  Use (partial positive) and (partial negative) to show charge distribution  Determine Shape of Molecule  Determine Polarity of Molecule

H2OH2OH2OH2O  1) Lewis & Bar?  2) Shape?  3) Polarity? O H H O—H H bent Polar—electrons distributed unequally

OF 2  1) Lewis & Bar?  2) Shape?  3) Polarity? O—F bent Nonpolar—electrons distributed equally O F F F

CF 4  1) Lewis & Bar?  2) Shape?  3) Polarity? tetrahedral Nonpolar—electrons distributed equally F C F F F F—C—F F F

Determining solubility: “Like Dissolves Like”  Polar compounds like water dissolve polar and ionic solids like NaCl  Nonpolar compounds like oils and fats dissolve other nonpolar compounds

Determining Solubility Examples: Are these pairs soluble?  HCl H 2 O  Both are polar, therefore they are soluble in each other. O—H H H—Cl

Determining Solubility Examples: Are these pairs soluble?  CF 4 NH 3  CF 4 is nonpolar, NH 3 is polar; therefore NOT soluble in each other. F—C—F F F H—N—H H

Practical Application: Solubility and the Human Body  Nonpolar compounds will be fat soluble and can be stored for later use.  Polar compounds will be water soluble and are passed in the urine if not used immediately.  For further reading to help with your spice project. s.html s.html