DCI for Electronegativity. Data Table:

Transcription

1 DCI for Electronegativity Data Table: Substance Ionic/covalent EN value EN Value EN NaCl ionic (Na) 0.9 (Cl) KBr (K) 0.8 (Br) 2.8 MgO (Mg) 1.2 (O) 3.5 HCl (H) 2.1 (Cl) 3.0 HF (H) 2.1 (F) 4.0 Cl 2 (O) 3.5 (O) 3.5 H 2 (H) 2.1 (H) Consider the three substances NaCl, HCl and Cl 2. Discuss the bonding in each of these three substances. In your discussion consider the following points; classify the type of bonding that occurs in each substance in the Table above; determine the EN for NaCl, HCl and Cl 2; what is the relationship of the EN and the type bonding; discuss the meaning of the magnitude of the EN, discuss the symmetry (symmetrical or not symmetrical) of the charge distribution in each substance.

2 2a) Which of the three substances, NaCl, HCl or Cl 2, does the substance CsF share the greatest similarity in terms of its bonding? Support your choice with a brief explanation. b) Which of the three substances, NaCl, HCl or Cl 2, does the substance O 2 share the greatest similarity in terms of its bonding? c) Which of the three substances, NaCl, HCl or Cl 2, does the substance FI share the greatest similarity in terms of its bonding? 3a) What does the arrow symbolize in the diagram below? Write a short explanation of what the arrow symbolizes in the diagram above: In your explanation use some or all of the following terms: covalent bond, polar covalent bond, nonpolar covalent bond, equal sharing of electrons, unequal sharing of electrons, electronegativity, difference in electronegativity, charge distribution, partial positive charge, partial negative charge, arrow/vector, dipole moment b) For each of the bonds between two atoms below, draw the bond and indicate how the arrow/vector is oriented? HCl ClBr OH NH CH CS ask clicker questions for HCl and OH then discuss polarity, then, Invent the idea of polarity put In clicker questions show three possible vector arrangements each direction and no vector and have the student pick.

3 4. Which of the following best represents the orientation of the vector you drew for HCl? HO? FF? PCl? 5. The following compounds have more than one bond. Draw the Lewis structure for each and add the arrows/vectors to represent the polarity of each of the bonds. Consider how these vectors interact with each other in these molecules? CS 2 OCS H 2 O BF 3

4 6. Which of the molecules is polar and which not polar? A) all polar B) all nonpolar C) CS 2 and OCS are polar D) CS 2 and H 2 O are polar E) OCS and H 2O are polar F) CS 2 and BF 3 are polar G) OCS and H 2O are nonpolar H) CS 2 and OCS are nonpolar

5 Instructor Comments: During class go to addition/vector- addition_en.html And demonstrate the vector addition for a linear molecule and a trigonal planar molecule. What is interesting about the EN values in the table from the BCE? SO we want the students to say that for covalent compounds there are two different values there is EN of 0 and a EN of not zero. Want is the Invent the terms polar bonds and nonpolar bonds; Show the electron distribution in O2 and HF and get students to discuss the bonds in terms of the EN. And what that means in terms of sharing the electrons. For O2 since EN is zero the two atoms share the electrons in the covalent bond equally, and we call that type of covalent bond a nonpolar bond What is the criteria for a nonpolar bond. What is the criteria for a polar bond. Relative strength of polar bonds Polar bonds have Charge distribution that is asymmetric (positive and negative) We use the term bond dipole to represent the magnitude of the polarity of the covalent bond. What happens if a compound contains many polar bonds? Can the compound be a polar compound or a nonpolar compound. What characteristics are present in polar compounds and nonpolar compounds? Look at the electron distribution of some molecules in Jmol. Look at CO 2 : Are the C- O bond polar or nonpolar? Since there is a nonzero EN the bonds have to be polar, so is the molecule polar or not polar, so we can represent the bond dipole using the standard vector notation, then show the bond dipoles and explain the molecular dipole. Use the vector- addition_en.jar file from phet to demonstrate the addition of vectors What a bond dipole is In 3a discuss the concept of a dipole moment. Useful thought: Use questions like 3a in the BCE and ACA, or from the list of terms below select all that apply to the diagram, or the definition, or the question.

6 ACA: Have student identify whether a list of compounds is polar or nonpolar. Give an image of H 2 CO and have students Give the student a formula like NH 3, ask what is the EN for each of the N- H bonds in NH 3. Is the N- H bond in NH 3 polar or nonpolar? Is the NH3 molecule polar or nonpolar. Give several additional compounds and ask if the compounds are polar or nonpolar. Provide students with a set of compound formulas and ask the students to indicate whether the compounds are polar or nonpolar. Ask student whether certain compounds are ionic, polar covalent or nonpolar covalent and predict strengths of ionic bonds comparing pairs of ionic compounds, and then rank order a set of four ionic compounds, with explanations of their order and comparisons (with two compounds). NOTES: Focus on the Intro the concept of polar covalent and nonpolar covalent molecules. Develop the ranges for EN for ionic, covalent and polar covalent molecules. Define ionic bonding; Show a model of an ionic compound (NaCl) Then discuss lattice energy; The chemical equation Show table of LE for Alkali halids and discuss Coulomb s Law and the reciprocal relationship of distance to LE.

7 Then look at LE for NaCl, MgCl2 and AlCl3 and discuss how charge is directly related to LE Substance Ionic/covalent EN value EN Value EN NaCl ionic (Na) 0.9 (Cl) KBr ionic (K) 0.8 (Br) MgO ionic (Mg) 1.2 (O) HCl covalent (H) 2.1 (Cl) HF covalent (H) 2.1 (F) Cl 2 covalent (O) 3.5 (O) H 2 covalent (H) 2.1 (H) 2.1 0