Presentation on theme: "Section 5.4—Polarity of Molecules"— Presentation transcript:
1 Section 5.4—Polarity of Molecules Objectivesexamine the trend of electronegativity on the periodic tableuse electronegativity to determine the polarity of covalent bonds
2 ElectronegativityElectronegativity is the attraction an atom has for the electrons it shares with another atom in a bond.Electronegativity has a periodic and group trend
3 Periodic Table with Electronegativies increasesdecreases
4 Polar BondsRecall from Sec. 5.1, that covalent bonds (where electrons are shared between 2 atoms) can be nonpolar or polar.In nonpolar covalent bond, electrons are shared equally but in a polar covalent bond, they are not shared equally.The electronegativity difference between the 2 atoms in the bond determines the type of covalent bond that forms.
5 Nonpolar: Two atoms sharing equally Each nitrogen atom has an electronegativity of 3.0.There is no electronegativity difference.They pull evenly on the shared electrons so, theelectrons are not closer to one or the other of the atoms.This results in a non-polar covalent bond.
6 Nonpolar: Atoms sharing almost equally CHElectronegativities: H = C = 2.5Electronegativity difference of each bond: 0.4The carbon pulls on the electrons slightly more (having a higher electronegativity), but the difference isn’t enough to create a polar bond.This is a non-polar covalent bond.
7 Polar: Two atoms share unequally COHElectronegativities: H = C = O = 3.5The C-H difference is 0.4; the C-O difference is 1.0.The C-H bonds are nonpolar.But, the oxygen atoms pulls significantly harder on the electrons than the carbon does. This is a polar covalent bond!
8 A polar covalent bond results in one end of the bond (and molecule) having a slight negative charge and one end having a slight positive charge.The atom having a higher electronegativity pulls the electrons closer to itself and, so, has a partial negative charge.The atom with the lower electronegativity has the electrons farther away and, so, has a partial positive charge.
9 Showing Partial Charges There are two ways to show the partial separation of chargesUse of “” for “partial”Use of an arrow pointing towards the partial negative atom with a “plus” tail at the partial positive atomCOH+-COH
10 Ionic BondsIonic bonds occur when the electronegativies of two atoms are so different that they can’t even share unevenly…one atom just takes them from the other
11 How to determine bond type Find the electronegativies of the two atoms in the bondFind the absolute value of the difference of their valuesIf the difference is 0.4 or less, it’s a non-polar covalent bondIf the difference is greater than 0.4 but less than 1.4, it’s a polar covalent bondIf the difference is greater than 1.4, it’s an ionic bond
12 If the bond is polar, draw the polarity arrow Let’s PracticeC – HO—FF—FC—ClExample:If the bond is polar, draw the polarity arrow
13 If the bond is polar, draw the polarity arrow Let’s PracticeC – HO—FF—FC—Cl2.55 – 2.2 = nonpolar3.44 – 3.98 = polar3.98 – 3.98 = non-polar2.55 – 3.16 = polarExample:If the bond is polar, draw the polarity arrow