Gizmo Polarity and Intermolecular Forces

Name: Gloria K. Tran Date: Student Exploration: Polarity and Intermolecular Forces Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. Vocabulary: dipole, dipole-dipole force, dipole-induced dipole force, electronegativity, intermolecular force, ionic bond, London dispersion force, molecule, nonpolar, nonpolar covalent bond, partial charges, polar, polar covalent bond, valence electron Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1.​ A big bully is having a tug-of-war with a small child. There is a ball attached to the middle of the rope. Toward whom will the ball move? ​ ​ ​ It will go towards the big bully due to strength. 2.​ Two equally strong kids are having a tug-of-war. What do you expect to happen to the ball in this situation? It will be balanced to due to the same strength. ​ ​ ​ ​ ​ ​ ​ ​ Gizmo Warm-up Just like in a tug-of-war, atoms that are bonded to one another pull on the electrons they share. In the Polarity and Intermolecular Forces Gizmo, you will explore how these opposing forces relate to bond types and the forces between molecules. To begin, drag the Na (sodium) and Cl (chlorine) atoms into the simulation area. Turn on Show valence electrons. A valence electron is found in the outermost energy level of the atom. 1.​ Click Play ( ). What do you notice? ​ ​ ​ ​ ​ ​ ​ ​ Cl and Na trade sizes and attract to eachother ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2.​ Which atom seems to be pulling more on the sodium’s one valence electron? ​ How do you know? ​ ​ Chlorine is pulling more on the sodiums one valence electron because chlorine is stronger. ​ ​ ​ ​ ​ ​ ​ ​ ​ 3.​ What happens to the colors of the simulated atoms, and what does this indicate? ​ ​ Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved Chlorine has the color red which is a stronger negativity and for sodiums blue means the amount of positive charge it has. Get the Gizmo ready: Activity A: ●​ On the BOND POLARITY tab, click Reset ( ●​ Drag the atoms out of the simulation area. Bond polarity ). Introduction: When atoms share electrons, their overall charge can be affected by the average position of the electrons. Polar bonds form when shared electrons are pulled closer to one atom than another, causing the bonded atoms to become partially charged. In nonpolar bonds, electrons are shared equally and the atoms remain neutrally charged. Question: What causes bonds to be polar or nonpolar? 1.​ Observe: Select the Show polar molecule inset checkbox. The animation shows the probable location of electrons (orange dots) in a polar molecule. A. What do you notice about the distribution of the electrons? The distribution of the electrons is uneven and being pulled more in one direction B. How does this electron distribution affect the charges of the bonded atoms? It creates the negative charge greater and the charges unbalanced 2.​ Observe: Turn on the Show nonpolar molecule inset. A. How are the electrons in this molecule distributed? The electrons are evenly distributed B. Why do the bonded atoms remain neutral? The bonded atoms remain neutral because the positive and negative pulls are even. 3.​ Experiment: Turn off Show polar molecule inset and Show nonpolar molecule inset. Check that Show valence electrons is turned on. Drag the Na and Cl atoms into the simulation area. Click Play. Note the colors. Red indicates a negative charge, while blue indicates a positive charge. A. What happens to sodium (Na) valence electron? It gets smaller positive charge. B.​ Try several other metal/nonmetal combinations. What do you notice about the bonds that form? The other combinations also show that the nonmetal pulls electrons strongly from the metals. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved​ ​ In ionic bonds, the nonmetal atom pulls electrons so much more strongly than the metal atom that electrons are completely transferred to the nonmetal atom. Drag each of these combinations into the Ionic bond bin on the upper right of the Gizmo. 4.​ Experiment: Now try forming bonds between different combinations of nonmetals. A. What do you notice? They come together to share electrons rather than on pulling more on the other. B. Are all of these bonds polar? Explain. These bonds are not polar due to none pulling stronger than the other which means it is equal. C. Which nonmetal appears to attract electrons the most? The nonmetal that appears to attract electrons the most is carbon ​ ​ 5.​ Experiment: Turn on Show electronegativity. Electronegativity (EN) describes how strongly an atom attracts a pair of shared electrons. The higher the EN value, the greater the tendency of an atom to hold onto electrons in a bond and become negatively charged. Electronegativity difference is found by subtracting the EN value of one atom from another. Choose two nonmetals with a small (or no) EN difference between them. Click Play. What happens to the shared electrons in this bond? ​ ​ ​ ​ ​ ​ In this bond, it has mostly an even charge (mainly pink) When the shared electrons experience the same attraction from each atom, the result is a nonpolar covalent bond. Drag the bonded atoms to the Nonpolar covalent bond bin. 6.​ Experiment: Choose two nonmetals with a large electronegativity difference. Click Play. What happens to the valence electrons in this bond? ​ ​ ​ ​ ​ ​ The valence electrons in this bond do not create as much as an even charge throughout the molecule (pink atom) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ A bond in which the electrons are shared unequally is a polar covalent bond. Notice the small δ+ and δ– symbols, which indicate partial charges. Drag the resulting combination to the Polar covalent bond bin. 7.​ Classify: Use the Gizmo to categorize the remaining element combinations as forming either ionic, polar covalent, or nonpolar covalent bonds. List your results below. Ionic Polar covalent Nonpolar covalent Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved​ ​ (EN difference > 1.67) MgO MgCl2 NaCl Na2O K2O KCl CaO CaCl2 (EN diff. < 1.67 and > 0.40) (EN difference < 0.40) NH3 H2O CO CO2 CCl4 OCl2 Activity B: Molecular polarity H2 O2 N2 CH4 NCl3 Get the Gizmo ready: ●​ Select the MOLECULAR POLARITY tab. Introduction: Ionic bonds, like those found in NaCl, form crystalline solids. Covalent bonds, on the other hand, usually form discrete molecules. A polar molecule, while neutral overall, has a slight positive charge on one end and a slight negative charge on the other. Question: What determines the polarity of molecules? 1.​ Observe: Notice that the molecules containing polar covalent bonds are grouped together at lower left, and the molecules containing nonpolar covalent bonds are at lower right. Drag the H2O molecule into the simulation area. A.​ Are the individual bonds in this molecule polar or nonpolar? ​ ​ ​ ​ ​ ​ ​ Polar B.​ Click Turn on electric field. What do you notice? ​ ​ I noticed that the oxygen is attracted to the positive side of the eclectic field and that hydrogen is attracted to the negative side of the field. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ C.​ The electric field consists of a positively charged plate on one side and a negatively charged plate on the opposite side. Which side of the H2O molecule is attracted to the positive plate, and why do you think this attraction occurs? The side with the oxygen is attracted to the positive plate due to oxygen being more electronegative than hydrogen and that opposites attract. D.​ Click Reverse field. Why does the H2O molecule rotate 180°? ​ ​ ​ Reversing the field causes the molecule to rotate so that the oxygen can face the positive side of the plate Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved​ ​ A polar molecule, such as H2O, changes its orientation when placed in an electric field. The positive end of the molecule is attracted to the negative plate, while the negative end is attracted to the positive plate. Drag this molecule into the Polar bin. 2.​ Observe: Drag the CH4 molecule into the simulation area. A. Do you think this molecule will rotate in the electric field? Why or why not? Due to methane being nonpolar, I don't think that this molecule will rotate. B. Turn on the electric field. Is this molecule polar or nonpolar? Methane is nonpolar Drag the CH4 molecule into the appropriate bin. 3.​ Classify: With the Gizmo, test and categorize the remaining molecules. Report your findings. Polar molecules Nonpolar molecules NH3 OCl2 CO NCl3 Cl2 CH4 N2 H2 O2 CCl4 CO2 Did the polarity of any of these molecules surprise you? Explain. ​ ​ ​ ​ Observing the diatomic gas you can also find out whether or not these molecules or polar or nonpolar. ​ ​ ​ ​ ​ ​ ​ ​ ​ 4.​ Explain: Drag the CCl4 molecule into the simulation area. ​ ​ ​ A. Does this molecule contain polar or nonpolar bonds? Polar Bonds B. Turn on the electric field. Why do you I think that this time it will not rotate because it contains think the molecule does not rotate in polar bonds this field? If a molecule is symmetrical, the effect of the partial charges on either side cancel out. In this case, even though it contains polar bonds, the molecule as a whole may be nonpolar. C. What other nonpolar molecule contains polar bonds? CO2 Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved​ ​ ​ ​ ​ 5.​ Challenge: Drag the OCl2 molecule into the simulation area. Turn on Show valence electrons. What do you notice at the very top of the oxygen atom, and how does this feature explain why the molecule is polar? In an OCl2 molecule, the top of the oxygen atom contains two lone pairs of electrons. This gives the oxygen end of the molecule a slight negative charge and the chlorine end a slight positive charge. Activity C: Intermolecular forces Get the Gizmo ready: ●​ Select the INTERMOLECULAR FORCES tab. Introduction: The polarity of molecules give rise to the forces that act between them. These intermolecular forces, or IMFs, affect many physical properties including boiling point, solubility, viscosity, and surface tension. Question: How does polarity affect the forces between molecules? 1.​ Observe: Select the Show polar molecules inset checkbox. What do you notice? ​ ​ I noticed that opposites attract even between molecules which is a dipole attraction. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Each polar molecule is known as a dipole. The attraction between the positive end of one dipole and the negative end of another is called a dipole-dipole force. 2.​ Observe: Turn on the Show nonpolar molecules inset. What do you notice? ​ ​ That the attraction is the same but temporarily becomes polar. Even when the molecules are nonpolar, random variations in the distribution of electrons can cause parts of these molecules to become slightly charged. This imbalance leads to very tiny, short-lived attractions between molecules called London dispersion forces. 3.​ Experiment: Turn off Show polar molecule inset and Show nonpolar molecule inset. Drag two H2O molecules into the simulation area, and click Play. Click Pause ( ) when you see an attraction (dotted line) form between molecules. Sketch the molecules, partial charges, and the attraction between them in the space to the right. ✏️ Why is a hydrogen atom in one H2O molecule attracted to the oxygen atom in an adjacent H2O molecule? Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved​ ​ Due to similar charges repel eachother while the opposites attract which creates the attraction in this example when they are adjacent. Drag the H2O-H2O molecule combination into the correct bin on the right. Which type of intermolecular force causes attraction between H2O molecules? ​ ​ ​ ​ Hydrogen bonding 4.​ Experiment: Drag two O2 molecules into the simulation area, but do not click Play yet. A. What force do you expect to see between O2 molecules? We would expect to see London dispersion forces B. Click Play and observe. What do you notice? I observed that the molecules together are non-polar due to them being temporarily polar the they are adjacent. C. Which force causes attraction between O2 molecules? The forces that cause the intermolecular bond are the London dispersion forces. 5.​ Experiment: Drag an O2 molecule and an H2O molecule into the simulation area. Click Play, and then click Pause when you see a bond form. A. What happens to the end of the O2 molecule that is closest to the positive end of the H2O molecule? The non-polar molecules when lined up with a polar molecule makes the non-polar molecule temporarily polar B. As the bond forms, does the polarity of the O2 molecule change? yes the polarity of the O2 molecule changes temporarily. it becomes a temporary dipole due to the influence of the polar H2O molecule. C. Classify this combination of molecules. (It might take a few tries to get it right.) Which type of intermolecular force is acting here? This combination is classified as dipole-induced dipole interaction. When a polar molecule approaches a nonpolar molecule, the electron cloud of the nonpolar molecule may become distorted, causing the nonpolar molecule to become temporarily polar. For example, if the negative end of the polar molecule approaches the nonpolar molecule, the electron cloud of the nonpolar molecule will be repelled, causing a slight positive charge at that end of the nonpolar molecule. The resulting attractive force is called a dipole-induced dipole force. 6.​ Classify: Drag out different combinations of molecules in the Gizmo and categorize them. Give at least three examples of molecule combinations for each intermolecular force. Dipole-dipole forces NCl3-OCl2 H2O-OCl2 Dipole-induced dipole forces H2O-O2 NH3-CO2 London dispersion forces O2-O2 CH4-CH4 Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved​ ​ NCl3-NCl3 CH4-NCl3 He-He 7.​ Summarize: Fill in the blanks to summarize the patterns you see. dipole dipole forces arise between polar molecules. london dispersion forces arise between nonpolar molecules. dipole induced dipole forces arise between polar and nonpolar molecules. Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved