Presentation on theme: "NELSON CHEMISTRY 12 SECTION 4.4 POLARITY What is the name of 007’s Inuit cousin? Polar Bond."— Presentation transcript:
NELSON CHEMISTRY 12 SECTION 4.4 POLARITY What is the name of 007’s Inuit cousin? Polar Bond.
Polar Bond Polar Bond: A bond in which one end is at least partially positive and the other end partially negative; due to a difference in electronegativity values between the bonding atoms.
Polar Bond Electronegativity (EN): The tendency to attract shared electrons within a bond. The “pulling power” that an atom has on electrons E.g. HCl: bonded electrons spend more time near Cl. EN: H = 2.20 EN: Cl = 3.16 stronger “pull”
Polar Bond If ∆EN isBond TypeDescriptionExample(s) 0Non-polar covalent Equal sharing of electrons within the bond N=N Cl ─ Cl >0 but <1.7Polar covalentUnequal sharing of electrons within the bond H ─ Cl C ─ F ≥1.7 or metal ─ non- metal IonicTransfer of electrons to more electronegative atom [Li] + [ Cl ] - [Mg] 2+ [ O ] 2-
Molecular Polarity Molecular Polarity: A difference in charge between sides of an entire molecule. If a molecule contains polar bonds, is it automatically a polar molecule? NO!! If it is symmetrical, it is non-polar. (The “pulls” cancel each other out.)
Molecular Polarity E.g. carbon tetrachloride (CCl 4 ) EN of C = 2.55 EN of Cl = 3.16 δ+δ+ δ¯ δ+δ+
Molecular Polarity E.g. beryllium hydride (BeH 2 ) EN of Be = 1.57 EN of H = 2.20 δ¯ δ+δ+
Molecular Polarity BUT….if a molecule is not symmetrical, it will be polar. E.g. ammonia (NH 3 ) EN of N = 3.04 EN of H = 2.20 δ¯ δ+δ+ δ+δ+ δ+δ+ δ+δ+ “net” dipole
Molecular Polarity E.g. dichloromethane (CH 2 Cl 2 ) EN of C = 2.55 EN of H = 2.20 EN of Cl = 3.16 δ¯ δ+δ+ δ+δ+ δ+δ+ δ+δ+ “net” dipole