Electronegativity and Bond Dipoles

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Imperial Valley College *

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101

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Chemistry

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Apr 3, 2024

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Relevant Course Level Learning Objectives: 3a and 3b Name: Page 1 of 5 Electronegativity and Bond Polarity This lab was adapted from Eichler, J. and Yezierski, E. Using Molecular Polarity PhET Simulation Concept Development for Understand Molecular Dipoles , 2020. Lab Learning Objectives: 1) To determine bond dipoles and partial charges 2) To examine how differences in electronegativity effect bonding type Use the PhET Simulation with CHROME available at: https://phet.colorado.edu/en/simulations/molecule-polarity 1. For all reactions in chemistry it is essential to start with a balanced chemical equation. Press the play button and then click on the “Two Atoms” simulation option. Click the Bond Dipole, Partial Charges, and Bond Character boxes, as well as the Electrostatic Potential. The bond dipole is an arrow that represents the electrostatic potential where the positive sign of the tail indicates the molecule has a partial positive charge ( +) and the tip of the arrow is indicating the side of the molecule where the tip is pointing as a partial negative charge ( -). The electrostatic potential will have cooler colors where there is a partial positive charge and warmer colors were there is a partial negative charge. 2. Set the both Atom A and Atom B to both have the less electronegativity (all the way to the left) and fill out the Bond character below. Then set Atom A and Atom B to both have the middle electronegativity (exact middle) and fill out the bond character below. Lastly set both Atom A and Atom B to have the more electronegativity (all the way to the right) and note the bond character below. Electronegativity Setting Bond Character Less Middle More 3. What can you say about the bond character if the electronegativity of Atom A and Atom B are the same?
Relevant Course Level Learning Objectives: 3a and 3b Name: Page 2 of 5 4. Return the electronegativity of Atom A and Atom B’s to “ less (all the way to the left). Then move Atom B’s electronegativity to the first mark to the right of less . Keep moving Atom B’s electronegativity towards “ more ”, stopping at each mark. What can you say about the bond dipole, the partial charges, the bond character and the electrostatic potential as the difference in electronegativity between two atoms increases? 5. Click on the Real Molecules simulation at the bottom of the screen. The Real Molecules is only available in Java so click the link when prompted. Once you download the simulation to your device, open the simulation and begin the activity. For each molecule be sure to have the bond dipoles, partial charges, atom electronegativities, and atom label boxes checked, as well as selecting the electrostatic potential. The molecules can be rotated which may make it easier to see the potential. Click and drag on the molecule to rotate. Fill in the first three columns of the table on the next page, skipping the last column (Bond Type) until #8: use the simulation to determine if bond dipoles are present within each molecule, sketch the Electrostatic Potential of the molecule, and record the difference in electronegativites between the two atoms.
Relevant Course Level Learning Objectives: 3a and 3b Name: Page 3 of 5 Molecule Electronegativity Difference between the two bonded atoms Are Bond Dipoles Present? Sketch the Electrostatic Potential Bond Type H 2 H-H HF H-F BF 3 B-F NH 3 N-H H 2 O H-O CO 2 C-O BH 3 B-H
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Relevant Course Level Learning Objectives: 3a and 3b Name: Page 4 of 5 6. In an ionic bond the electron is transferred from one atom to another. In a covalent bond the electrons are shared, but as we can see from above the electrons are not always shared equally. If the electrons are unequally shared, we say that the bond is polar covalent. To determine the bond type we need to look at Electronegativity. What is the definition for electronegativity and what are the periodic trends for electronegativity by group and period on the periodic table? Cite your source. 7. Electronegativity is actually an energy. Compare the definition you found above to one definition that uses the Mulliken scale where EN= ½(IE + EA), the average of ionization energy and electron affinity. Are they similar? 8. To determine the effect of Electronegativity Difference on Bond Type, we can use the table below. Please note this Electronegativity difference is an approximation and may vary depending on the source you use. Electronegativity Difference (ΔEN) Bond Type Small ~(<0.4) Covalent Intermediate ~(0.4 2.0) Polar Covalent Large ~(>2.0) Ionic Go back to #4 and fill in the Bond Type column according to the table above.
Relevant Course Level Learning Objectives: 3a and 3b Name: Page 5 of 5 9. Using the chart of electronegativity values, what are the bond types of each of these bonds and draw the electrostatic potential, bond dipole arrows and charges (if the bond has them) for Li F, N N, and N F . Element Electronegativity Value Li 1.0 F 4.0 N 3.0