P2.-Polar-and-Non-Polar-Molecules (1).pptx

science

1. POLAR AND NON-POLAR MOLECULES

2. OBJECTIVES: Determine if a molecule is polar and non-polar given its structure. Relate the polarity of a molecule to its properties.

3. POLARITY In chemistry,  polarity  is a separation of electric charge leading to a  molecule  or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end.

4. Polar and Nonpolar Bonds There are two types of covalent bonds Nonpolar Covalent Bonds (equal share of electrons) Polar Covalent Bonds (unequal share of electrons)

5. 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

6. Nonpolar Covalent Bond A Nonpolar Covalent Bond is an equal sharing of electrons between two atoms ( Cl-Cl , N-N, O-O)

7. 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

8. Practice What type of bond is HCl ? (H = 2.1, Cl = 3.1) Difference = 3.1 – 2.1 = 1.0 Therefore it is polar covalent bond.

9. 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) 0.9 Polar Covalent 0 Non-Polar Covalent 2.0 Ionic 1.5 Polar Covalent Covalent 2.3 Ionic 1.9 Non-polar Covalent

10. 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-

11. Polar Molecules Molecules with 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.

12. 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

13. Symmetrical Molecules Because of symmetry, molecules that have polar bonds are overall a nonpolar molecules (+ and – charges cancel out or balance out) Examples: CO 2 BF 3 CCl 4

14. Dipole 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

15. 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)

16. The properties of a substance depend in part on it’s polarity Polar Compounds Stronger intramolecular forces. Form ions when dissolved in water. Higher melting and boiling points. Conduct electricity in water. Non-polar Compounds Weak intramolecular forces. Do not form ions. Lower melting and boiling points. Do not conduct electricity.

17. “Like dissolves like” Polar compounds will dissolved other polar compounds, but not non-polar compounds. Can you think of any examples?

18. 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.

19. ACTIVITY 2 Decide whether the molecules represented by the following formulas are polar or nonpolar. (You may need to draw Lewis structures and geometric sketches to do so.) OF 2 CH 2 Cl 2 HCN SO 2 C H 4