Science with Tara

Question

Which row shows the correct structures of the covalent molecules C₂H₂; hydrazine, N₂H₄; nitrogen, N₂ and oxygen O₂?

Note

At O levels, we learnt 2 types of bonds – covalent and ionic.

Covalent bond is formed when electrons are shared between non-metals.

Ionic bond is formed when metal transfers its electrons to non-metals.

In this question, we will focus on covalent bond.

Click here for more notes on chemical bonding.

Focus – Covalent bond

After bonding, each atom attains the noble gas electronic configuration.

Elements and compounds with covalent bonds are called molecules. A molecule is a group of two or more atoms held together by covalent bonds.

In accordance with the syllabus objectives, students must be able to describe, using ‘dot-and-cross’ diagrams, the formation of covalent bonds between non-metallic elements.

We will go through in detail, the drawing of 5 different covalent substances in this video, namely hydrogen, oxygen, water, methane and carbon dioxide. From there, we will determine the structural formula of each substance.

Knowing how to write accurate structural formula is particularly important when students deal with Organic Chemistry. We will lastly draw dot and cross diagram of the covalent substances in this question – ethyne, hydrazine, nitrogen and oxygen.

GCE O level, Singapore, 2012/P1/Q9

Topic: Chemical Bonding, O Level Chemistry, Singapore

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