Polarity

Polar Covalent Remember ionic bonds transfer electrons, while covalent bonds share electrons. All atoms do not attract their electrons in a bond to the same degree. One can determine the degree to which electrons are transferred or shared using the electronegativity difference

Polar Covalent Remember…electronegativity is a measure of an atom’s ability to attract the pair of electrons it shares with another atom. In general, metals have lower electronegativities than non metals Each atom’s electronegativities has been determined by experiences and can be found in your textbook on pg 71.

EN Differences To find ΔEN, subtract the EN of 2 atoms. EN must be a real number. (ie. No negatives!) If the ΔEN is: = an ionic bond = polar covalent = non polar covalent Determine the classification of these bonds: A) B & PB) S & OC) Li & OD) Mg & N =0.15 non polar=0.86 polar=2.46 ionic=1.73 ionic

Polar vs Nonpolar Covalent Nonpolar Covalent Bonds Between two atoms with similar EN Electrons are shared equally between the two Nuclei from each atom are attracting the electrons with equal force There is little or no positive & negative charges present Polar Covalent Bonds Between two atoms with moderate difference in EN Electrons are not shared equally Results in a localized negative and positive charge The atom with higher EN will be slightly negative and other will be slightly positive Bigger the difference, the more polar the bond

Dipole Moments In polar molecules, we indicate their positive or negative partial charges using δ - and δ + and their polarity or “dipole moment” H δ+ F δ- H δ+ O δ- Dipole Dipole moments occur when there is an instant in time when the electrons are distinctly unequally shared.

Polar Molecules In addition to bonds being polar or non polar, so can molecules based on their shape. If polar bonds are present, to determine if a molecule is polar, we look at its shape and whether or not it is symmetrical.

Polar Molecules Polar Molecule Water is polar because the lone pair pushes the bonded pair together and so the molecule is not symmetrical (Asymmetrical) Non Polar Molecule All the hydrogens in methane are pulling at the same strength (same EN) so the molecule is symmetrical

Which molecules are polar? (Indicate partial charges for polar molecules) a) NI 3 b) SiCl 4 c) CHCl 3 ΔEN = 0.38 = non-polar Bonds δ+ δ- Asymetrical, but NO POLAR BONDS! Non-polar Molecule ΔEN = 1.26 = Polar Bonds δ- Symmetrical, non- polar molecule ΔEN C-Cl = 0.61 = Polar Bonds ΔEN H-C = 0.35 = non-polar Bonds δ+ δ- Asymetrical, with polar bonds, polar molecule

Polar vs Nonpolar Characteristics Molecule Type Molecule Shape Forces of Attraction Relative Melting/ Boiling Point Soluble in H 2 O PolarLess symmetry Relatively Strong Relatively High Yes Non PolarHigh Symmetry WeakVery lowNo