Chapter 9 Notes – Part II Mr Nelson 2009

Warm Up – ionic, molecular or acid HBr Chlorous Acid FeS Copper(I) fluoride PBr5 dinitrogen dioxide K2SO4 nitrogen monoxide CCl4 hydroiodic acid HNO3 potassium nitrate LiCl phosphoric acid

Resonance Draw the Lewis dot structure for ozone, O3.

Resonance But this is at odds with the true, observed structure of ozone, in which… …both O-O bonds are the same length. …both O-O bonds have the same strength

One Lewis structure cannot accurately depict a molecule like ozone. We use multiple structures, resonance structures, to describe the molecule.

Resonance Example HCO2-

Electrons that form the second C-O bond in the double bonds below do not always sit between that C and that O They move among the two oxygens and the carbon.

Exceptions to the Octet Rule Three situations with exceptions to the octet rule: When Ions or molecules have: an odd number of electrons less than an octet (B & Al) more than eight valence electrons (an expanded octet)

Exceptions! Boron and Aluminum are okay with only 6 e- around them BF3

More Than an Octet PCl5 can only exist is if phosphorus has 10 electrons around it. Presumably d orbitals in these atoms participate in bonding.

Different Bond Types Ionic (extremely polar) Covalent Electrons are transferred Covalent Polar – uneven sharing of electrons Nonpolar – even sharing of electrons

Nonpolar Covalent Bonds

Polar Covalent Bonds

Ionic Bonds

Electronegativity Electronegativity is the ability of atoms in a molecule to attract electrons to themselves. On the PT, EN increases: …from left to right across a row. EN decreases …from the top to bottom of a group (column).

Bond Properties and Electronegativity

Bond properties and electronegativity Any bond can be classified by subtracting the EN of the 2 elements involved High differences in electronegativity (1.7 – 4) make the bond IONIC Low differences (0-1.7) make the bond COVALENT: Polar covalent – 0.4 – 1.7 Nonpolar Covalent – 0 – 0.4

Polar Covalent Bonds Electrons are not always shared equally in compounds. Oxygen pulls harder on the electrons it shares with hydrogen than hydrogen does. Oxygen’s end of the molecule has more electron density than the hydrogen end.

Nonpolar, polar, and ionic bonds (a) – a nonpolar covalent bond (b) – a polar covalent bond (c) – an ionic bond

Polar Covalent Bonds When two atoms share electrons unequally, a bond dipole results.

Polar Covalent Bonds The greater the difference in electronegativity, the more polar is the bond.