Electronegativity and Polarity Chem 332 – O’Dette

How do you determine the polarity of a molecule? Based on polarity of bonds and shape of the molecule Depends on the electronegativity of the elements in the molecule

What is electronegativity? Ability of an element to attract electrons Look up the values in a table “Tug of War”

Electronegativity Difference Polarity of Bonds Type of Bond Electronegativity Difference Between Atoms Nonpolar Covalent 0 – 0.4 Polar Covalent 0.5 – 1.8 Ionic 1.9 – 3.3

Polarity of Covalent Bonds Nonpolar Covalent What happens with the electrons in a nonpolar covalent bond? Electrons are shared equally between the atoms EX: H2 H – H H : H Electronegativity H = 2.1 H = 2.1 Difference = 0

Polarity of Covalent Bonds Polar Covalent What happens with the electrons in a polar covalent bond? Electrons are shared unequally between the atoms EX: HBr H – Br: H : Br Electronegativity H = 2.1 Br = 2.8 Difference = 0.7 : Br has a stronger pull on the electrons

Polarity of Ionic Bond Ionic What happens with the electrons in a ionic bond? Electrons are completely transferred Ex: NaCl

: Polarity of Molecules NH3 vs. CO2 H – N – H : O = C = O : H Is it possible to have a compound with polar bonds in it but for the compound itself to be nonpolar? NH3 vs. CO2 H – N – H : O = C = O : H : Electronegativity N = 3 H = 2.1 Difference = 0.9 Electronegativity C = 2.5 O = 3.5 Difference = 1 Polar Bond Polar Bond Polar Molecule Nonpolar Molecule

Polarity of Molecules Even if the bonds between atoms are polar, the overall molecule polarity is nonpolar if There are no lone pairs on central atom Elements surrounding central atom are the same

: Concept Check What is the polarity of the following molecule? COS : S = C = O : : Polar