O-Level Chemistry: Question on Chemical Bonding

Hi Everyone,

Today, i am going to share with you an exam-based (similar to GCE O-Level Pure Chemistry Examinations) question that my students asked me recently in the weekly Secondary 4 Chemistry Tuition Class.

Let’s take a look at the question below.

Question:

Which of the following substance contains both Ionic & Covalent bonds?

A. HCN

B. NaNO₃

C. MgO

D. CH₃COOH

Suggested Solutions:

Now, first you must understand the difference between Ionic and Covalent Bondings.

In Ionic Bonding, there is always strong electrostatic forces of attraction that holds the oppositely charged ions (cation and anion) together.

In Covalent Bonding, there is always strong covalent bonds that holds the atoms together.

Next, you need to be able to determine either the structural formula or the dot-and-cross diagram of the substance.

Option A: HCN would have a structure that consists of CH single covalent bond and CN triple covalent bond. Pure Covalent Bonding.

Option C: MgO is an Ionic Compound whereby the oppositely charged ions of [Mg]²⁺ and [O]^2- are held together by strong electrostatic forces. Pure Ionic Bonding.

Option D: CH₃COOH is a carboxylic acid and if you draw out the structure, you will see that it is made up of covalent bonds. Pure Covalent Bonding.

Option B: NaNO₃ is an Ionic Compound whereby the oppositely charged ions of [Na]⁺ and [NO₃]^– are held together by strong electrostatic forces. However, do note also that in the [NO₃]- polyatomic ion, the N and O atoms are held together by strong covalent bonds. Take a rough paper and draw the structure or dot-and-cross diagram out. You will get it. Thus, NaNO₃ has both Ionic and Covalent Bonds!

Answer is Option B.

I am sure you have learned something useful today.

Feel free to share it with your friends who need help in Basic Chemistry.

Cheers! 🙂

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