Read the pages indicated by A-6 in the text, examine the table showing bonding patterns of atomic compounds and study behavioral objectives 19-21. A second type of bonding is covalent bonding. Instead of transferring electrons from one atom to another which occurred during ionic bonding, the outer shell electrons (valence electrons) are shared between the two atoms. When atoms share electrons there is no electromagnetic charge between the atoms. The rules for how many electrons which can be shared is the same as the number of electrons which can be transferred discussed earlier for ionic bonding. Atoms share enough electrons to fill (2 or 8) its outer shell. Carbon has four valence electrons and hydrogen has one valence electron; therefore each carbon must share four electrons to end with eight in order to fill its valence shell and each hydrogen must share one electron to end with two electrons in order to fill its valence shell. If a single carbon atom was to react with hydrogen to form a stable molecule, four hydrogen atoms would be required to provide the four shared electrons. The carbon would have a total of eight electrons in its outer shell and each hydrogen would have two electrons in its outer shell. The molecular formula for this compound would be CH₄. 

 In your notes draw a diagram showing the arrangement of electrons between the carbons atom and the hydrogen atoms. 

 Press here to check answer. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Organic molecules and organic chemistry refers to the fact that these molecules must contain the element carbon. There are other atoms that may share electrons with hydrogen, oxygen, etc.; however, in this course you will only be dealing with carbon. In other words for testing purposes in this course, if carbon is present in the molecules than covalent bonding will prevail, if carbon is not present than ionic bonding will prevail. Some organic molecules will contain covalent bonding in one part of the molecule and ionic bonding in a different part of the molecule. 

2. Ions are formed during covalent bonding. 

a) true 

b) false 

 The bonds formed by sharing two electrons (in the case above one from the carbon atom and one from the hydrogen atom) is called a single covalent bond. Carbon will always have four covalent bonds. When you draw carbon with covalent bonds it must always have four sets of shared electrons. 

                           | 
                        -C- 
                          | 

Study the figures showing carbon with covalent bonds included in the readings. Each of the four covalent bonds of carbon will have two electrons which it shares with the atom to which it is bonded. 

3. How many covalent bonds will hydrogen have? 

                         H- 

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4. How many covalent bonds will oxygen have (it has six valence electrons)? 

                        O=    Or    -O- 

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5. Answer behavioral objective 20 by finding the number of outer shell  electrons and determining the number of covalent bonds formed. Finish filling in the chart below. 

 

Element	Number of valence          electrons	Number of covalent bonds
Carbon
Hydrogen
Oxygen
Nitrogen
Phosphorus
Sulfur

 
Press here to check your answer. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

  
Examine behavioral objective 21. The problems below will demonstrate to you how the atoms of an organic molecule (covalent bonding)  must be arranged and the difference between the molecular formula and structural formula. 

6. How many hydrogen atoms are needed to form a stable molecule containing six carbons? Remember each carbon must have four bonds and each hydrogen only one bond. 

C-C-C-C-C-C 

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7. How many hydrogen atoms are needed to form a stable molecules containing the following skeleton? Remember each carbon must have four bonds, each oxygen must have two bonds  and each hydrogen only one bond. 

                             C-C-C-O 

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8. What group is attached to this molecule? 

                                 H H H 
                                  |   |   | 
                             H-C-C-C-O-H 
                                  |   |   | 
                                 H H H 
 Press here to check your answer. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

  
Molecular formula is the number atoms of each element present in a molecule. 
               ethanol = C₂ H₆ O 
 
Ethanol  contains two carbon atoms and 6 hydrogen atoms and one oxygen atom. 
 
 

Structural formula is the structure showing how the atoms are arranged in the molecule. 
                                      H  H 
                                       |    | 
                  ethanol  =  H-C-C-O-H 
                                       |    | 
                                      H  H 
 
Ethanol contains two carbon atoms attached to one another, one oxygen atom attached to the end carbon and hydrogen atoms attached to the outside atoms. 

Write the definition for the molecular and structural formula in your notes. 

9. Is there any other way these atoms could be arranged and still have all of the atoms with the correct number of covalent bonds and the same molecular formula? 

 Press here to check your answer. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

  
10. What is the structural formula for C₂ H₇N? 

                             H H H 
                             |   |    | 
                        H-C-C-N-H 
                             |    | 
                            H  H 

                          or 
 

                            H  H  H 
                             |    |    | 
                        H-C-N-C-H 
                             |        | 
                            H      H 

Press here to check your answer. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

  
Both of these are correct. They both have the same molecular formula but different structural formula. Such molecules are called isomers. Write out the answer for behavioral objective 21. 

 A short hand method of drawing structural formulas is: 

           H H H H H 
           |   |   |   |   | 
     H- C-C-C-C-C-H             or     CH₃ CH₂ CH₂ CH₂ CH₃  
           |   |   |   |   | 
          H H H H H 
 

             H H H H 
              |   |   |   | 
         H-C-C-C-N-H             or  CH₃ CH₂ CH₂ NH₂ 
              |   |   | 
             H H H 

Compare the actual structural formula to its shorthand counter part. (learn how to write both ways). 

Double and Triple Covalent Bonds 
Some molecules have two atoms being held together with two or three covalent bonds. Examine figures of molecules with double covalent bonding in your text (A-6). 

Single covalent bonds are the most stable. However it is possible for double and tripe covalent bonds to form between atoms. Molecules containing double and triple covalent bonds are not as stable. 

C₂H₆    =              H H 
                             |    | 
                        H-C-C-H  or   CH CH 
                             |   |                 3     3 
                            H H 
 
The molecule  above contains all single covalent bonds (7 to be exact). 
 

C₂ H₄     = 
 
                        H-C=C-H     or   CH₂ =CH₂ 
                             |    | 
                            H  H 
 
The molecule above contains one double bond and  four single bonds. 
 
11. How many single and double covalent bonds are found in the molecule below? 

           CH₃-CH=CH-CH₂-OH 

Press here to check answer. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

12. Draw a structural formula for the compound listed below and indicate the number of single and double covalent bonds. 

                        C₃ H₆ O 
 
  Press here to check answer. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

  
This is the end of lesson four. Biological molecules mostly consist of molecules with covalent bonding. These molecules are carbon skeletons (chains of carbon) with different groups attached. These functional groups will be introduced in the next lesson. Click here to go to Miniunit Alpha Lessons Page and continue on to the next lesson, functional groups.  

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