Covalent Bonding Polar Bonds and Molecules Covalent Bonding -- Polar Bonds and Molecules -Bond Polarity • “The Tug of War” – The pairs of electrons that are bonds between atoms are pulled between the nuclei of the atoms in a bond. – The electronegativities of the atoms determine the winner. • Classifications for Bonds – Nonpolar covalent • When atoms pull the bond equally • Happens with two atoms of equal electronegativity, most often using the same atoms • Examples: H2, O2, N2 – Polar covalent • When atoms pull the bond unequally • Happens with two atoms of different electronegativities • Example: HCl, HF, NH Covalent Bonding -- Polar Bonds and Molecules -Bond Polarity • • In a polar molecule, one end of the molecule is slightly more electronegative than the other atom, resulting in one atom being slightly negative (-) because of higher electronegativitiy, and the other atom being slightly positive (+) because of lower electronegativity. is known as a partial charge since it is much less than 1+ or 1- charge. Covalent Bonding -- Polar Bonds and Molecules -Bond Polarity • Electronegativities and Bond Types – H: 2.1 Cl: 3.0 Since hydrogen is less, it will have the positive partial charge while chlorine has the negative partial charge. – 3.0 – 2.1 = 0.9 HCl is polar covalent. 0.0 – 0.1 difference Nonpolar covalent bond H – H (0.0 difference) 0.1 – 1.7 difference Polar covalent bond H – Cl (0.9 difference) 1.7 + difference Ionic bond Na+Cl- (2.1 difference) Covalent Bonding -- Polar Bonds and Molecules -Polar Molecules • • Dipole – Molecule that has two poles – Example: HCl from the previous page Polar vs. Nonpolar H2O and CO2 Both have 3 atoms; yet, One is polar and one is nonpolar. Why? Structure (with bond polarity) determines the molecules polarity. 3 video clips coming up QuickTime™ and a Sorenson Video 3 decompressor are needed to see this picture. QuickTime™ and a Sorenson Video 3 decompressor are needed to see this picture. QuickTime™ and a Sorenson Video 3 decompressor are needed to see this picture.