Polar Bonds and Polar Molecules (Chemistry 1)

Polar Bonds and Polar Molecules (Chemistry 1)

• 1.
  Aim: What arepolar bonds and polar molecules?
• 2.
  Polar and NonpolarBonds • There are two types of covalent bonds • Nonpolar Covalent Bonds (equal share of electrons) • Polar Covalent Bonds (unequal share of electrons)
• 3.
  Polar Covalent Bond •A Polar Covalent Bond is unequal sharing of electrons between two atoms (H-Cl) • In a polar covalent bond, one atom typically has a negative charge, and the other atom has a positive charge
• 4.
  Nonpolar Covalent Bond •A Nonpolar Covalent Bond is an equal sharing of electrons between two atoms (Cl-Cl, N-N, O-O)
• 6.
  Classification of Bonds Youcan determine the type of bond between two atoms by calculating the difference in electronegativity values between the elements The bigger the electronegativity difference the more polar the bond. Type of Bond Electronegativity Difference Nonpolar Covalent 0  0.4 Polar Covalent 0.5  1.9 Ionic 2.0  4.0
• 7.
  Practice What type ofbond is HCl? (H = 2.1, Cl = 3.1) Your Turn To Practice  N(3.0) and H(2.1)  H(2.1) and H(2.1)  Ca(1.0) and Cl(3.0)  Al(1.5) and Cl(3.0)  Mg(1.2) and O(3.5)  H(2.1) and F(4.0) Difference = 3.1 – 2.1 = 1.0 Therefore it is polar covalent bond.
• 8.
  How to showa bond is polar • Isn’t a whole charge just a partial charge • d+ means a partially positive (less electronegative) • d- means a partially negative (more electronegative) • The Cl pulls harder on the electrons • The electrons spend more time near the Cl H Cl d+ d-
• 9.
  Polar Molecules • Moleculeswith a positive and a negative end • Requires two things to be true  The molecule must contain polar bonds This can be determined from differences in electronegativity. Asymmetric molecule.
• 11.
  Symmetrical Molecules • Becauseof symmetry, molecules that have polar bonds are overall a nonpolar molecules (+ and – charges cancel out or balance out) • Examples: • CO2 BF3 • CCl4
• 12.
  Asymmetrical Molecules • Ifa molecule has polar bonds (and there is no symmetry to cancel out + and – charges), the molecule is polar. • Examples: • H2O HCl • NH3
• 13.
  Dipole When there isunequal sharing of electrons a dipole exists Dipole is a molecule that has two poles or regions with opposite charges A dipole is represented by a dipole arrow pointing towards the more negative end
• 16.
  Practice Drawing Dipoles P-Br P = 2.1 Br = 2.8 P –Br + - Practice  H(2.1) – S(2.5)  F(4.0) - C(2.5)  C(2.5) - Si(1.8)  N(3.0) – O(3.5)
• 17.
  Is it Polar? •HF • H2O • NH3 • CF4 • CO2
• 18.
  Summary • In apolar bond, one atom is more electronegative than the other. • In a nonpolar bond, both atoms have similar electronegativities. • An asymmetric molecule with polar bonds is a polar molecule. • An asymmetric molecule with nonpolar bonds is a nonpolar molecule. • A symmetric molecule, regardless of the polarity of the bonds, is always a nonpolar molecule.