Covalent Bonding Explained

What is a covalent bond?

All you have to remember is: Covalent Bonding = Sharing Electrons

In the world of chemistry, a covalent bond is like a friendly handshake between atoms. By sharing a pair of electrons between two atoms, a covalent bond is formed. 

The concept of covalent bonding has evolved over centuries. The term "covalent bond" was first introduced by Irving Langmuir in 1919, building on Gilbert N. Lewis's earlier work on electron pairs and bonding. Lewis's depiction of atoms and molecules using dot structures to represent electrons revolutionised our understanding of chemical bonding.

Why share their electrons, you may ask? When they share, both atoms end up with a full outer shell, which makes them stable (and happy!) Each covalent bond provides one extra shared electron for each atom. Every atom tries to form enough covalent bonds to fill its outer shell. When atoms make covalent bonds with one or more atoms, they form a molecule.  

A visual tip: For shared electrons, we always use a dot and a cross. The number can go up depending on what combination of atoms is asked in the exam. Usually, you are only required to draw the outer shell of electrons. 

Let’s look at the 4 examples below, and you will smash this section in no time!

1) Hydrogen

Hydrogen is a solo dancer who just needs one more friend to feel complete!

If you check the periodic table, Hydrogen only has one atom. Therefore, they only need one electron to complete the outer shell. So, two hydrogen atoms share their single electrons to form a single covalent bond. Each hydrogen atom now has a full outer shell of 2 electrons, making a stable H2 molecule. 

2) Hydrogen Chloride

Chlorine is almost happy but just needs one more friend to be fully content!

There are 2 elements that form Hydrogen Chloride—Hydrogen and Chlorine. If we know that Hydrogen has one atom, we need to know how many atom/atoms Chlorine has in its outer shell. Chlorine has 7 electrons in its outer shell. What does this mean? 7 is an odd number, which DOES NOT make Chlorine happy as it is not stable. Chlorine needs one more electron to complete its outer shell. How can we make it happy? Hydrogen and Chlorine can share one electron each to form a single covalent bond.  This way, Hydrogen and Chlorine both achieve a full outer shell, forming a stable Hydrogen Chloride molecule. 

3) Oxygen

Oxygen likes to form a duo and needs two dance partners!

Oxygen has 6 electrons in its outer shell. Since Oxygen stands for O2, they will need to share some electrons. Oxygen needs two more electrons to complete its outer shell. Two oxygen atoms share two pairs of electrons ( a total of 4 electrons) to form a double covalent bond. Each oxygen atom now has a full outer shell, making a stable O2 molecule.

4) Carbon Dioxide

Carbon is the social butterfly and needs 4 partners to feel stable!

Carbon dioxide stands for CO2, meaning there is one carbon atom and 2 oxygen atoms. Carbon has 4 electrons in its outer shell, and Oxygen has 6 electrons in its outer shell. In this case, the 2 oxygen atoms will need to share electrons with a carbon atom. Remember, oxygen has 6 electrons in its outer shell. Now let’s look at carbon—it has 4 electrons in its outer shell. If carbon is sandwiched in between, it would need 4 electrons to survive, be stable and happy. Therefore, Carbon needs 4 more electrons to complete its outer shell, and each oxygen atom needs 2 more electrons. Carbon forms 2 double bonds, one with each oxygen atom, sharing 2 pairs of electrons with each oxygen. 

Practice Drawing Covalent Bonds

Try drawing the outer shells and shared electrons for the following molecules to clarify your understanding:

1. Methane (CH₄) - Carbon shares one electron with each of four hydrogen atoms. Methane, a primary component of natural gas, is formed by carbon sharing electrons with four hydrogen atoms. It serves as a significant energy source and plays a role in organic chemistry.

2. Water (H₂O) - Oxygen shares two electrons with two hydrogen atoms. Water, the essential molecule for life, consists of two hydrogen atoms covalently bonded to one oxygen atom. This simple molecule is crucial for biological processes, from hydration to photosynthesis.
   

3. Nitrogen (N₂) - Two nitrogen atoms share three pairs of electrons. Nitrogen gas, making up about 78% of Earth's atmosphere, consists of two nitrogen atoms sharing three pairs of electrons. This triple bond gives nitrogen its remarkable stability.

Remember, the key to mastering covalent bonding is practice and visualising the shared electrons! Happy bonding!

Answers: