3.1b Covalent Bonds Lab

3.1b Covalent Bonds Lab Name VOCABULARY: covalent bond, diatomic molecule, Lewis diagram, molecule, noble gases, nonmetal, octet rule, shell, valence, valence electron PRIOR KNOWLEDGE QUESTIONS 1.) There are eight markers in a full set, but Flora and Frank each only have seven markers. Flora is missing the red marker, and Frank is missing the blue marker. What can they do so that each has a full set of markers? Frank can share his marker with Flora and Flora can share her marker with him. 2.) Otto and Olivia each have six markers. Otto is missing the purple and green markers, and Olivia is missing the black and brown markers. What can they do so that each has a full set? Otto can share his markers with Olivia, and Olivia can share her markers with Otto GIZMO WARM-UP Just like the students described above, nonmetal atoms can share electrons. As you will see in the Covalent Bonds Gizmo™, atoms form bonds in this way. To begin, check that Fluorine is selected from the Select a substance menu. Click Play ( see the electrons orbiting the nucleus of each atom. ) to 3.) The outermost electrons in each atom are called valence electrons. How many valence electrons does each fluorine atom have? 4.) Click Pause ( 7 ). Drag an electron from the left atom to the right atom. Click Play. What Happens? The ones that were dragged now orbit both atoms. 5.) Click Pause, drag an electron from the right atom to the left, and then click Play. What happens now? A pair of electrons now orbit both atoms. ACTIVITY A: SHARING ELECTRONS: • Get the Gizmo ready: Click Reset. Select Hydrogen. Introduction: The electrons that orbit the nucleus of an atom are arranged into shells. The first shell contains up to two electrons and the second contains up to eight electrons. Most elements are stable when they have eight valence electrons—a rule of thumb known as the octet rule. (Elements with less than five electrons are stable with two valence electrons.) QUESTION: What happens when atoms share electrons? 6.) Predict: Each hydrogen atom has one valence electron, but it needs two electrons to be Each hydrogen stable. How can both hydrogen atoms each achieve a stable configuration? atoms can contribute its one electron to share a pair. 7.) Form a bond: Drag the electrons so that they move around both hydrogen atoms. Click Play to observe them in orbit, and then click Check. You have created a covalent bond. Congratulations, you have completed a molecule of hydrogen! Because the molecule has two atoms, it is a diatomic molecule. 8.) Draw a diagram: Covalent bonds are shown in Lewis diagrams. In a Lewis diagram, dots represent unshared valence electrons and dashes represent pairs of shared electrons. Turn on Show Lewis diagram. What is the Lewis diagram for hydrogen, H2? (OR Draw on a separate sheet of paper and scan in with this worksheet.) H:H 9.) Form a bond: Now select Fluorine and create a molecule of fluorine, F2. What is the Lewis diagram for fluorine, F2? (OR Draw on a separate sheet of paper and scan in with this worksheet.) Page 1 of 4 .. .. :F - F: .. .. 10.) Think and discuss: How is the formation of covalent bonds similar to kids sharing markers? How is it different? If possible, discuss your answer with your classmates and teacher. Covalent bonds are like kids sharing markers because both atoms share electrons, however unlike the kids, the atoms share those electrons forever. ACTIVITY B: BUILDING MOLECULES: • Get the Gizmo ready: Click Reset. Turn off Show Lewis diagram. Select Oxygen. QUESTION: How do atoms share more than one pair of electrons? 11.) Observe: Like fluorine and most other elements, oxygen atoms are most stable with a full complement of eight valence electrons. A. How many valence electrons does each oxygen atom have now? B. How many more electrons does each oxygen atom need to be stable? 6 Needs 8 12.) Form a bond: Drag electrons back and forth until the molecule of oxygen (O2) is stable. Click Check to confirm your molecule is stable. A. How many pairs of shared electrons are there in a stable molecule of oxygen? 2 Pairs 13.) Practice: Create covalent bonds and stable molecules for the remaining substances. Draw Lewis diagrams for each one. (Draw on a separate sheet of paper and scan in with this worksheet.) a.) Oxygen .. .. O= O .. .. :N ≡ N: b.) Nitrogen c.) Chlorine d.) Water e.) Carbon dioxide .. .. :Cl - Cl: .. .. .. :O - H | H .. .. .. O=C=O .. .. .. f.) Ammonia Page 2 of 4 g.) Methane H | H-N-H .. H | H-C-H | H 14.) Count: Review the Lewis diagrams you drew on the previous page. Note that each element tends to form a certain number of chemical bonds. This value is the valence of the element. Also, the oxidation state. The sum should be 2 or 8, to obey the Octet Rule. For each element in the table below, use the Gizmo to find the number of valence electrons and the list the valence based on the Lewis diagram. Then find the sum of these numbers. Element Symbol # of valence electrons Valence Sum a.) Fluorine F 7 1 8 b.) Hydrogen H 1 1 2 c.) Oxygen O 6 2 8 d.) Nitrogen N 5 3 8 e.) Chlorine Cl 7 1 8 f.) Carbon C 4 4 8 g.) Silicon Si 4 4 8 15.) Make a rule: If you knew the number of valence electrons in a nonmetal atom, how would you determine the valence of the element? (Hint: Ignore hydrogen for now.) For a nonmetal, you can determine its valence by subtracting the number of valence electrons from 8. 16.) Analyze: The first shell can hold a maximum of two electrons. How does this explain the valence of hydrogen? Hydrogen's valence is 1 because its first shell can hold only 2 electrons 17.) Apply: Selenium has six valence electrons. What is the valence of selenium? 2 18.) Think and discuss: The last column of the periodic table contains the noble gases, elements that do not easily form chemical bonds. Why don’t these gases tend to form chemical bonds? Page 3 of 4 Noble gases rarely form chemical bonds because their outer shells are full and stable. ASSESSMENT: Complete the Assessment questions in Explore Learning and below: 1. 3 2. 6 3. 4 4. Diagram D 5. Diagram D Page 4 of 4