Dipole - Electronegativity - Nonpolar covalent bond - Partial charges - Polar covalent bond - Polarity -

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1 Chemistry Electronegativity & Polarity Guided Inquiry (Textbook 10.3) Use your knowledge of chemical bonding, the textbook, your classmates, the PhET simulation and the internet to answer the questions and learn about electronegativity, polarity and bonding. Essential Questions Why are bonds usually neither purely covalent nor purely ionic? How can we use electronegativity to determine the polarity of a bond? How do electronegativity and molecular shape determine the polarity of a molecule? Vocabulary write the definitions for each word. Dipole - Electronegativity - Nonpolar covalent bond - Partial charges - Polar covalent bond - Polarity -

2 Types of Bonds (Review) In the introduction to this unit we learned about the 3 types of bonds: Ionic Bond The transfer of electron(s) between two atoms to create a cation and an anion that are held together by the attraction of their opposite charges. Covalent Bond The sharing of two, four or six electrons between two atoms. The sharing of electrons holds the two atoms together. Metallic Bond Metal cations held in fixed positions by a sea of electrons. We ll focus on ionic and covalent bonds as we learn about electronegativity and bond polarity. Molecule Polarity Simulation Run the Molecule Polarity simulation from the PhET web site: polarity. Select the Two Atom tab at the top of the screen. Set the View parameters to show the bond dipole, partial charges, and bond character. Set the Surface parameters to show electron density. Turn the electric field off. Play with the simulation to try different combinations of electronegativity for atom A and atom B. Watch what happens to the 4 parameters: bond dipole, partial charges, bond character and electron density. 1. What affects the 4 bond parameters: the electronegativity of each atom or the difference in electronegativity between the two atoms? 2. Why? 3. How does the electronegativity affect the: a. electron density of the bond?

3 b. strength of the dipole? c. strength of the partial charges? 4. Does the electronegativity of the atoms affect the bond parameters? 5. Based on your observations what is the relationship between the atoms electronegativities and the character of the bond (i.e. covalent, ionic or a mix of the two)? 6. In a pair of bonding atoms which atom has the: a. highest electron density? b. positive partial charge? c. the negative end of the dipole? 7. What is bond polarity?

4 Bond Types, Electronegativity & Polarity Nonpolar Covalent Bonds the difference in electronegativity between the two atoms is 0.4 or less. The electrons are shared equally. This usually only happens when two atoms of the same element bond together. For example, the bond between the two atoms in diatomic molecules such as H 2, N 2, O 2, F 2, Cl 2, I 2 and Br 2 is purely covalent because there is no difference in electronegativity. Ionic Bonds the difference in electronegativity between the two atoms is 1.8 or more. The electron(s) is transferred from the less electronegative atom to the more electronegative atom. Ionic bonds are usually between a group 1 or group 2 metal and a non- metal. For example, the bond between the atoms in NaCl, MgO and KCl are ionic because there is a large difference in electronegativity. Polar Covalent Bonds the difference in electronegativity between the two atoms is between 0.4 and 1.8. This difference is enough to cause an unequal sharing of electrons, but not a complete transfer of an electron from one atom to the other. These bonds will have a positive and negative end. Polar covalent bonds are usually between non- metals. For example, the bonds in H 2 O, CO 2, PCl 5 and SO 3 are polar covalent. Drawing Polar Bonds - We show the positive and negative ends of polar bonds in one of two ways as shown to the right. The drawing on the left uses partial charges. You place the δ- by the more electronegative atom and the δ+ by the less electronegative atom. The drawing on the right uses the dipole moment. You place the positive end of the arrow by the less electronegative atom and the tip of the arrow by the more electronegative atom.

5 8. Use your knowledge of electronegativity, bonding and polarity to classify and draw the following bonds: Bonding Atoms Electronegativity Draw Bond Showing: Atom #1 Atom #2 Difference Bond Type Partial Charges Dipole H & H N & N O & O F & F Cl & Cl H & C H & N H & O H & Cl C & N C & O C & F P & O S & O Na & Cl Li & F Mg & Cl Mg & O Zn & Cl Zn & O

6 9. Compare and contrast nonpolar covalent bonds and polar covalent bonds. 10. Compare and contrast a polar covalent bond and an ionic bond.