Electronegativity + – 0 0 H Cl H H

The basic units: ionic vs. covalent Ionic compounds form repeating units. Covalent compounds form distinct molecules. Consider adding to NaCl(s) vs. H2O(s): Cl Na Cl H O Na Cl Cl Na Na H O H O NaCl: atoms of Cl and Na can add individually forming a compound with million of atoms. H2O: O and H cannot add individually, instead molecules of H2O form the basic unit.

I’m not stealing, I’m sharing unequally We described ionic bonds as stealing electrons In fact, all bonds share – equally or unequally. Note how bonding electrons spend their time: H2 HCl LiCl H Cl [Li]+ [ Cl ]– H + – 0 + – covalent (non-polar) polar covalent ionic

I’m not stealing, I’m sharing unequally Point: the bonding electrons are shared in each compound, but are not always shared equally. The greek symbol  indicates “partial charge”.

Electronegativity Electronegativity is “a number that describes the relative ability of an atom, when bonded, to attract electrons”. The periodic table has electronegativity values. We can determine the nature of a bond based on EN (electronegativity difference). EN = higher EN – lower EN Example NBr3: EN = 3.0 – 2.8 = 0.2 (for all 3 bonds).

Electronegativity a EN Again, it is a grey scale not black and white below 0.5 = covalent 0.5 - 1.7 = polar covalent above 1.7 = ionic Again, it is a grey scale not black and white Determine the EN and bond type for these: HCl, CrO, Br2, H2O, CH4, KCl

Electronegativity Answers HCl: 3.0 – 2.1 = 0.9 polar covalent CrO: 3.5 – 1.6 = 1.9 ionic Br2: 2.8 – 2.8 = 0 covalent H2O: 3.5 – 2.1 = 1.4 polar covalent CH4: 2.5 – 2.1 = 0.4 covalent KCl: 3.0 – 0.8 = 2.2 ionic

Homework Read pg 278-286 in textbook