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Covalent Bonds assignment answer key
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Student Exploration: Covalent Bonds
Vocabulary: covalent bond, diatomic molecule, Lewis diagram, molecule, noble gases, nonmetal, octet rule, shell, valence, valence electron
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
- 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 red marker
with Flora and Flora can share her blue marker with frank.
- 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? Olivia can share her purple and green markers with otta and otta can share his black and brown markers with olivia.
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 ( ) to see the electrons orbiting the nucleus of each atom.
- The outermost electrons in each atom are called valence electrons. How many valence
electrons does each fluorine atom have? Each fluorine atom has seven valence electrons.
- Click Pause ( ). Drag an electron from the left atom to the right atom. Click Play. What
happens? The electrons that was dragged now orbits both atoms.
- 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.
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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?
Predict: Each hydrogen atom has one valence electron, but it needs two electrons to be stable. How can both hydrogen atoms each achieve a stable configuration?
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. Click the camera ( ) icon to take a snapshot of your completed molecule. Right-click the image, and click Copy Image. Paste the image into a blank document and label the image “H 2 .”
- 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, H 2? H - H
- Form a bond: Now select Fluorine and create a molecule of fluorine, F 2. Take a snapshot of this molecule and add it to your document. (Be sure to label each molecule you add.)
What is the Lewis diagram for fluorine, F 2? : F- F:
- 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. The children like sharing markers, atoms will share electrons to obtain a complete set of eight valence electrons. This allows them to form a chemical bond. Covalent bonds are different because any valence electrons may be shareed.
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Activity B:
Building molecules
Get the Gizmo ready:
∙ Click Reset. ∙ Turn off Show Lewis diagram. ∙ Select Oxygen.
Activity B (continued from previous page)
- 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.
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
Fluorine F 7 1 8
Hydrogen H 1 1 2
Oxygen O 6 2 8
Nitrogen N 5 3 8
Chlorine Cl 7 1 8
Carbon C 4 4 8
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 most elements, valence is equal to eight minus the number of valence electrons.
Analyze: The first shell can hold a maximum of two electrons. How does this explain the valence of hydrogen? Hydrogen has one valence electron and needs one more valene electrons to complete the first shell.
Apply: Selenium has six valence electrons. What is the valence of selenium? Two
Think and discuss: The last column of the periodic table contains the noble gases , elements that do not easily form chemical bonds.
Whydon’t these gases tend to form chemical bonds? Most noble gases all contain eight
valence electrons( helium contains two) They already have a full set of valence electrons so
they do not need to share or borrow valence electrons to become stable. Therefore, they do
not form chemical bonds. 2019
Covalent Bonds assignment answer key
Course: Organic Chemistry II (CHEM 273)
