!..!.. : F F :! Chem Level 3: Lewis Dot Diagram activity : Name Page 1

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1 hem Level 3: Lewis Dot Diagram activity : Name Page 1 Part 1: This Activity will help you learn to draw Lewis Dot Diagrams/Structural s for molecules. pen the web site : lick Diatomics on the website. lick on F 2. lick on the bond and electron boxes to make the dot diagram. See how it works? lose the box. Use the same steps to draw the dot diagrams for the other molecules. ( Molecules obeying octet rule ). You can check your answers using the website. Part 2 (Later): Model Making (on the Right): VSEPR Theory uses the dot diagrams to determine the shapes of molecules. In your dot diagram: ircle the Bonding electron regions in red. ircle the non-bonding electron pairs in blue. ount the pairs and use the VSEPR hart to determine the geometry (shape) of these molecules. See H 2 as an example. dot diagram/ structural Electron groups Electron Pair, bond, Non-! bond Drawing F = 14!..!.. : F F :! XXXX l 2 XXXX H Tetrahedral bent NH 3 H 4 l 2 (Not on site) l 4

2 These molecules have double or triple bonds. All are on the website. A Double or Triple bond counts as! Page 2 one Bonding Electron group on the VSEPR chart. Use SPRINGS to make these models! 2 xygen gas N 2 Nitrogen gas 2 arbon dioxide σ π dot diagram/ structural Electron groups, bond, Non-! bond XXXX Electron Pair XXXX Drawing: Make Model What s the difference between the dot diagram for 2 and the dot diagram for H 2 (Page 1)? Why is one and the other bent? HN Hydrogen yanide Now that you can (hopefully) draw a Dot Diagram, let s try some more challenging molecules and polyatomic ions. For the polyatomic ions, add /electrons (for negative charges) or subtract / electrons (for positive charges). (all on website except Br 2 ) dot diagram/ structural dot diagram/ structural H NH 2 S 2 NH 4 + N Br 2 (Not on site)

3 hem Level 3: More Lewis Dots Page 3 The following dot diagrams are incorrect. What s wrong with them? a. : l = l :!..!.. b. :H S :!!!..!.. c. H H!!!.. d. H!!! Resonance: Some molecules are even more complicated. Resonance is a term used when you can draw 2 or more equilivalent dot diagrams for a molecule. Most involve a double bond that you can move from place to place. Try zone, 3, in clase as an example. hemists believe the actual molecule is in between the resonance structures, like a 1.5 bond but we can t draw a dot diagram to show that! All are on the Website. dot diagram/ structural s (each resonance form) dot diagram/ structural s (each resonance form) 3 N 2 N Exceptions to the octet Rule: There are many molecules that exist, but don t follow the every atom wants 8 outer electrons rule. Some examples are shown below. You need to recognize them, but you won t have to draw them on your own. n the right, which ones are exceptions, and what type? dot diagram Type of exception dot diagram Type exception/ normal? N 6+5 =11!... : = N : odd number of electrons 2!..!!.. : = = : BF =24 : F B F :!!! : F : electron deficient or less than octet l 2!..!.!.. : l :! Pl 5 around l omitted for clarity = 40! l! l! \ / l P l!!!! l More than octet XeF 4 omitted around F! F! F! \.. /! Xe! /! \!! F! F

4 More Model Making: Electron Groups, Electron Pair and! Page 4 are determined around each arbon atom separately. Formula, Name 4. H 2 formaldehyde dot diagram/ structural Electron groups around each arbon, bond, Non-! bond Electron Pair Drawing Look back at NH 3 (Page 1). Why is its different from H 2? 2 H 6 ethane 2 H 4 ethene 2 H 2 Acetylene 5. 4 H 10 n butane straight 5. 4 H 10 iso butane branched 6. HBrlF Bromochloro fluoromethane (make 2) 6a. HBrlF Bromochloro fluoromethane (mirror image)

5 Bond Polarity Table: opy this table on the back your VSEPR chart! Page 5 Type of Bond Non Polar covalent Polar covalent Ionic Sharing of electrons? Equal Sharing Unequal sharing Electron Transfer harge Distribution? Even Uneven positive and negative ions electronegativity difference? small (0 to 0.2) medium (0.3 to 1.8) large (1.9 and up) Types of atoms, example Picture, δ+, δ- atoms? Data Table 1 Atom A H a H Electroneg. value Atom B H N N usually same element (non-metals) F F Electroneg. value usually 2 different nonmetals Elect. difference δ+ δ usually metal + nonmetal Example, math F-F, = 0 -l, = 0.61 Na + l, = 2.23 Types of Bond Polarity: We can determine the Type of Bond by comparing the Electronegativity values for each atom. Electronegativity is the tendency for an atom to attract electrons to itself in a bond. Higher values (4) attract electrons more, lower values (0.7) attract electrons less. Look up the electronegativity values (on the back of your Periodic Table) for the atoms in Data Table 1. Subtract these numbers and record the difference. Predict if the bond is Nonpolar, Polar or Ionic, using the criteria in the Table above. Which atom (if either) is slightly negative (higher electronegativity) or positive (lower eneg.)? pen the java app molecule_polarity_en.jar l Non polar, Polar, Ionic +δ Atom - δ Atom bond Now let s use this app to check your predictions. lick n the Partial charges, Bond character, and Electrostatic Potential buttons. Slide the electronegativity sliders for Atom A and B to approximately match the values you looked up. What type of bond results? Were your predictions correct? lick on the Electric Field. You can spin the bond around to see what happens in an electric field. 1. In a bond, which atom has the slightly negative charge (δ ), the atom with the higher or Lower electronegativity? Why do you think this happens? 2. As the colors of the atoms get brighter, what does that tell you about the polarity of the bond?

6 3. What happens to a Polar bond in an external Electric field?! Page 6 4. What happens to a Non-Polar bond in an external Electric field? Polarity is an extremely important concept that affects many properties of materials. Is the whole molecule (not just the individual bond) Polar or Non-polar? This activity will show you how to predict Polarity, and how it is affected by bond polarity and molecular geometry. lick on the 3 Atom tab in the molecular polarity app. Try the various scenarios listed in Data Table 2. Adjust the electronegativity sliders for each atom (less, middle, more). lick n the Dipole and Electric Field buttons. To test the Polarity of the molecule, you can spin the molecule around to see what happens in an electric field. You can also adjust the angle for atom A or to make a bent or molecule. Data Table 2 : Atom A Atom B Atom Non polar, or Polar bond? (Shape) Non Polar (mostly) or Polar Molecule? mid mid mid mid mid mid Bent less mid less less mid less Bent less mid more less mid more Bent 1. Do non-polar bonds always result in a Non-Polar molecule? Explain, using examples from your results. 2. Do Polar bonds always result in a Polar molecule? Explain, using examples from your results. 3. If the bonds are Polar, how does geometry (shape) influence Polarity? Explain, using examples from your results. 4. What happens to the Polarity if the atoms around the central atom have different electronegativities? Explain, using examples from your results.

7 Polarity continued Page 7 Real Molecules : Let s apply what you just learned. This flowchart (Also on the back of your VSEPR chart) will help you to predict the Polarity of molecules. Step 1: Are the Bonds Non-Polar? If Yes: the Molecule must be Non-Polar. Skip to Result, fill in Non-Polar. STP!! If No (Polar bond) go to step 2. Step 2: Are there Different atoms around the central atom? If Yes, the molecule must be Polar. Skip to Result, fill in Polar. STP! If No (same atom around center) go to step 3. Step 3a: Find the geometry (shape) of the molecule (You made them on Page 1, 2 and 4) Step 3b: Is it a Non-Polar shape? (3 atom, trig. planar, tetrahedral)? Result = Non-Polar molecule! or a Polar shape (2 atom, bent, trig. pyramidal)? Result = Polar Molecule Data Table 3: 1. You looked up electronegativity values and determined Bond Polarities on page 5. 3a. Look at the shapes you drew on page 1, 2 and 4. Molecule 1. Non polar 2. Different 3a. 3b. Non-Polar or Result: Non Polar heck? bonds? atoms around (shape) Polar Shape? (mostly) or Polar Y/N center? Y /N Molecule? BF 3 N N Trig Planar NP Non-Polar 2 HN H 2 NH 3 H 4 2 H 2 XXXXX pen the Real Molecules tab on the app and check your predictions. Make sure you understand any mistakes you made. 5. Explain why BF 3 is Non-Polar, even though its bonds are Polar. 6. Explain why H 2 is Polar, even though it has a Non-Polar shape. 7. Put it all together: Get a model kit and make 3 H 8. Sketch a drawing in the space below. What is the electronegativity difference between and H?. Polar or Non-Polar Bond? Use your VSEPR chart. What is the molecular geometry around each arbon? Do you predict this molecule is Polar or Non-Polar? Why? Drawing of 3 H 8 Model

8 Level 3 hem Review sheet for ovalent Bonding Page 8 1. Fill in the following chart for these molecular compounds. Molecule Dot Diagram/Structural Drawing Molecule Polar or Non Polar a. H 2 Se b. H 2 l 2 c. l d. H 2 e. 2 H 2 H H 2. What is the electronegativity difference of the H Br bond? Is the bond polar, non-polar or ionic? Which atom is more positive (if any)? 3. Which of these would exhibit Resonance? Draw the other resonance form(s). Which are exceptions to the octet rule? How many electrons are on the central atom? Which are just plain wrong? What s wrong with them?! a. : = S :!!! f. : :!.. b. H l :!..!.!.. g. : S l S :!!!!..!.. c. :H S :!! h. : = = :!!!..!....!.. d. : F Kr F :!!! i. : H!! e. : = S :!!! : :! j. :Br Be Br :!! 4. In Q 3, What is the molecular geometry, polarity and number of sigma and pi bonds for : a., e., f., h., j. 1. a. bent, P; b. tetra., P, c. lin, P; d. trig. plan., P ; e. lin., NP; , P, H; 3. res= a, e; except= d (10), g (7), j (4); wrong = c. (16, should be 11, 4 around H), i. ( 14, should be 11) ; b, f, h = normal; 4. a. bent, P, 2 σ, 1 #; e. trig plan, NP, 3 σ, 1 #; f. lin, P, 1 σ, 2#; h. lin., NP, 2σ, 2#; j. lin, NP, 2σ.

9 ovalent Bonding Matching Practice Name! Page 9 Which of these molecules fit the following descriptions? Section 1 1. Has a tetrahedral shape 2. Is a 3 atom Linear molecule 3. Exception to octet rule, odd number of electrons 4. Has a Triple covalent bond 5. Has Ionic bond(s) a. l l b. H 4 c. al 2 d. : :!..!.!.. e. : = N :.. 6. Has Non polar covalent bond(s) f. = = Section 2: For this section, choose all molecules that apply. And Molecules may be used more than once! 7. ontains two sigma and one pi bond 8. Has polar bonds, but is a non-polar molecule 9. ontains 1 sigma and 2 pi bonds 10. Has a trigonal planar, bent shape 11. Is incorrect. 12. Is a polyatomic ion. 13. Exhibits resonance 14. Is an exception to the octet rule, more than octet c. a. : : b.! l! l l!! l..!..! :..! N H..! d. F.. Xe : F e. : Br Be Br :!..!.. f. [ :..!..! Br..!..!..: ] g. [..!..!.. :! = N.. : ] 15. Is an exception to the octet rule, less than octet 1. b; 2. f; 3. e; 4. d; 5. c. 6 a. ; 7. g; 8. b, e; 9 a; 10. g; 11 c; 12 f, g; 13. g; 14. d; 15 e