Forming Molecular Compounds with Covalent Bonds

Did you know that only molecular compounds are composed of molecules?


Ionic compounds are composed of large three-dimensional arrays of alternating ions, while molecular compounds are composed of individual discrete molecules. These individual molecules are formed when two non-metals bond together. They both need to gain electrons to complete their octets. The only way this can be achieved is if they share their valence electrons. The bond formed by sharing electrons is called a covalent bond.


B4.35 Two fluorine atoms sharing pair of electrons


There are a vast number of compounds that exist as molecules: from a relatively simple water molecule to more complex structures such as vitamin B9 (folic acid).


B4.37 Sharing electrons in a water molecule



© Wikipedia
B4.38 Vitamin B9


What these compounds have in common is the sharing of valence electrons to create stable octets.

Study these two examples to strengthen your understanding of the covalent bond.

Ammonia: In each molecule of ammonia, NH3, one nitrogen atom shares electrons with three hydrogen atoms. This way, they all attain full valence energy levels. Note that since the first energy level is the valence for hydrogen, it only needs two electrons instead of the usual eight.


B4.39 Nitrogen atom sharing electrons with three hydrogen atoms


Carbon tetrafluoride: Its formula is CF4. In each molecule, one carbon atom shares electrons with four fluorine atoms.


B4.40 Carbon atom sharing electrons with four fluorine atoms

  Digging Deeper


B4.36 Two oxygen atoms sharing two pairs of electrons

B4.36a Two nitrogen atoms sharing three pairs of electrons


Two atoms can share more than just one pair of electrons. For example, two oxygen atoms can bond and create stable octets by sharing four electrons; this is called a double bond: O=O.

Two nitrogen atoms share six electrons to create an octet. This is a triple bond: «math xmlns=¨http://www.w3.org/1998/Math/MathML¨»«mi mathvariant=¨normal¨ mathcolor=¨#FFFFFF¨»N«/mi»«mo mathcolor=¨#FFFFFF¨»§#8801;«/mo»«mi mathvariant=¨normal¨ mathcolor=¨#FFFFFF¨»N«/mi»«/math».

  Interactive Activity

Covalent Bonding Tutorial @ ChemThink

This interactive slideshow will model the attractions in molecules. Only work through slides 1 to 13 of the 35 slides.

Click the procedure tab to continue. 

  1. Click on the play icon to open the tutorial. The tutorial can also be accessed at https://quick.adlc.ca/attraction
  2. Read slides 1 and 2.
  3. Move the atoms toward one another. Continue moving them around, slowly.

    Describe what happens when one atom is brought closer to the other.

    The second atom becomes attracted and moves toward the first atom, but it always remains the same distance apart

    Describe what happens when you continue to move the one atom around slowly.

    The second atom “follows along” or is attracted to the first atom and remains the same distance apart, if you move it slowly.

    Why do you think this happens?

    There is an attraction between the two atoms. The electrons of one atom are attracted to the nucleus of the neighbouring atom and vice versa.
  4. Read slides 3 to 13.

  Read This

Please read pages 46 to 48 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on the formation of covalent bonds by non-metallic atoms. Remember, if you have any questions or you do not understand something, ask your teacher!

  Practice Questions

Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.

  1. Covalent bonds are formed by the _____ of electrons.

    Covalent bonds are formed by the sharing of electrons.
  2. What types of elements form covalent bonds?

    non-metallic
  3. Using modified Bohr diagrams, model the covalent bonds that will form in a molecule of oxygen difluoride (OF2).


    B4.41 Oxygen atom sharing electrons with two fluorine atoms