Chapter 6 -1 Bond Polarity (p. 198 – 201) Covalent bonding = shared electrons but, do they share equally? Electrons are pulled, as in a tug-of-war, between the atoms nuclei When the atoms in a bond are the same, the electrons are shared equally (as in diatomic molecules), and the bond that results is called a nonpolar covalent bond

Nonpolar Covalent Bond e- are shared equally symmetrical e- density usually identical atoms

Electronegativity The attraction of an atom for shared pair of electrons is called its electronegativity. Fluorine has the greatest electronegativity. The metals have low electronegativities.

Electronegativity Table (p. 198) Increases up and to the right.

Bond Polarity When two different atoms bond covalently, there is an unequal sharing of electrons the more electronegative atom will have a stronger attraction for the shared electrons, and will acquire a slightly negative charge called a polar covalent bond, or simply polar bond.

+ - Polar Covalent Bond e- are shared unequally asymmetrical e- density results in partial charges the positive and minus signs (with the lower case delta ) denote partial charges. d+ d- + -

Electronegativity Atom with higher e-neg  - Atom lower e-neg  +

Figure 6-7, p.199 shows how the electronegativity difference can indicate the type of bond that tends to form

Bond Polarity Consider HCl H = electronegativity of 2.1 Cl = electronegativity of 3.0 the bond is polar the chlorine acquires a partial negative charge, and the hydrogen a partial positive charge

Bond Polarity Only partial charges, much less than a true 1+ or 1- as in ionic bond Written as: H Cl d+ d-

Bond Polarity H Cl Can also be shown: the arrow points to the more electronegative atom. H Cl

Polar molecules A polar bond in molecules composed of only 2 atoms makes the entire molecule “polar” HCl has polar bonds, thus is a polar molecule. a molecule in which one end has a partial positive charge and the other end has a partial negative charge is called a dipole

Learning Check Identify the type of bond between the following atoms A. K-N 1) nonpolar 2) polar 3) ionic B. N-O 1) nonpolar 2) polar 3) ionic C. Cl-Cl 1) nonpolar 2) polar 3) ionic

Polar molecules The effect of polar bonds on the polarity of the entire molecule depends on the molecular shape carbon dioxide has two polar bonds, but is linear:

Nonpolar Molecule BF3 F B

Polar Molecule H2O H O

Polar molecule CHCl3 H Cl

Nonpolar Polar Ionic