Polar Bonds and Polar Molecules.pptx

For Grade 11 General Chemistry Class

1. GENERAL CHEMISTRY 1

2. POLARITY OF SIMPLE MOLECULES LIEZL E.. VALIENTE Teacher III Bangui National High School

3. Objectives: determine the electronegativity differences among atoms in a given compound ; predict the polarity of simple molecules based on molecular geometry; identify polar and non-polar molecules based on molecular geometry’s symmetrical and asymmetrical orientation Infer the relevance of Molecular Polarity in real life applications on chemical reactions

4. Covalent Bond bond forms from non metal –non metal when atoms share one or more pairs of electrons. -happens when the difference between the electronegativities of the atom is not enough to an electron to transfer.

5. Polar and Nonpolar Covalent Bonds In the nonpolar covalent bond of H 2 , electrons are shared equally. In the polar covalent bond of HCl , electrons are shared unequally.

6. Polar and Nonpolar Bonds Nonpolar Covalent Bonds (equal share of electrons) Polar Covalent Bonds (unequal share of electrons )

7. Nonpolar Covalent Bond A Nonpolar Covalent Bond is an equal sharing of electrons between two atoms (Diatomic-H 2 , N 2 , F 2 , Cl 2 ) The 7 diatomic elements are  hydrogen (H), nitrogen (N), oxygen (O), fluorine (F), chlorine (Cl), bromine (Br), and iodine (I) .

8. Nonpolar Covalent Bond

9. Polar Covalent Bond A Polar Covalent Bond is unequal sharing of electrons between two atoms (H-Cl) and H 2 O

10. Classification of Bonds You can 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  0.4 Polar Covalent 0.5  1.9 Ionic 2.0  4.0 The higher the electronegativity, the more desperate for an electron the atom is .

11. Electronegativity and Types of Bonds

12. The polarity of a bond— the extent to which it is polar —is determined largely by the relative electronegativities of the bonded atoms. Electronegativity is  a chemical property that describes the tendency of an atom or a functional group to attract electrons toward itself . 

13. Practice What type of bond 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. Nonpolar Polar Ionic Polar Ionic Polar

14. Bond Polarity and Dipoles When there is unequal 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 The positive and negative ends are represented by the Greek letter delta, with a + or − charge.

15. How to show a 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-

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) H – S  +  - C(2.5) - Si(1.8) N(3.0) – O(3.5) F– C  -  + C– S  -  + N –O  +  -

17. Polarity of Molecules—Nonpolar In a nonpolar molecule , all the bonds are nonpolar . Molecules such as H 2 , Cl 2 and CH 4 are nonpolar because they contain only nonpolar bonds.

18. Polarity of Molecules—Nonpolar A nonpolar molecule also occurs when polar bonds (dipoles) cancel each other because of a symmetrical arrangement. Molecules such as CO 2 and CCl 4 contain polar bonds with dipoles that cancel each other out.

19. Nonpolar compounds  will be symmetric, meaning all of the sides around the central atom are identical - bonded to the same element with no unshared pairs of electrons.

20. Polarity of Molecules—Polar A polar molecule - Requires two things to be true The molecule must contain polar bonds This can be determined from differences in electronegativity. Asymmetric molecule. Any molecule with lone pairs of electrons around the central atom is polar . dipoles from individual bonds do not cancel each other out.

21. Polarity of Molecules—Polar Examples of polar molecules include HCl , H 2 O, and NH 3 . HCl is linear and contains a polar bond. H 2 O is bent and contains two polar bonds as well as two lone pairs on oxygen.

22. Polarity of Molecules—Polar NH 3 is trigonal pyrimidal , and contains three polar bonds and a lone pair on nitrogen.

23.   The molecular geometry of a molecule affects its polarity. Each CO bond has a dipole moment, but they point in opposite directions so that the net CO2 molecule is nonpolar. In contrast, water is polar because the OH bond moments do not cancel out .

24. Guide to Determination of Polarity of a Molecule

25. Solution Determine if the molecule OF 2 is polar or nonpolar. Step 1 Determine if the bonds are polar or nonpolar covalent. Oxygen has an electronegativity of 3.5, and fluorine has an electronegativity of 4.0. O—F bonds are polar covalent. Difference = 4.0 – 3.5 = 0.5 Therefore it is polar covalent bond.

26. Solution Determine if the molecule OF 2 is polar or nonpolar. Step 2 If the bonds are polar covalent, draw the electron-dot formula and determine if the dipoles cancel. Dipoles in O—F bonds do not cancel; the molecule is polar.

27. Symmetrical Molecules Because of symmetry, molecules that have polar bonds are overall a nonpolar molecules (+ and – charges cancel out or balance out) Example: CO 2

28. Asymmetrical Molecules If a molecule has polar bonds (and there is no symmetry to cancel out + and – charges), the molecule is polar. Examples: H 2 O HCl NH 3

29. Examples on Board: Freon-12 (CCl 2 F 2 ) Dichloroflouromethane (CHCl 2 F ) Carbon tetraBromide (CBr 4) Sulfur tetraOxide (SO 4 )

30. Compounds Dipole moment Bond Classification 1. HF 2. H 2 O - 3. NH 3 -

31. Compounds Dipole moment Bond Classification 4. CF 4 5. CO 2

32. Summary In a polar 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.

33. Compounds Dipole moment Bond Classification 1. HF 2. H 2 O - 3. NH 3 - Polar Polar Polar

34. Compounds Dipole moment Bond Classification 4. CF 4 5. CO 2 Non-Polar Non-Polar