Home / iGCSE Chemistry 0620 Extended – 2.5 Simple molecules and covalent bonds- Exam Style Questions Paper 2

iGCSE Chemistry 0620 Extended - 2.5 Simple molecules and covalent bonds- Exam Style Questions Paper 2- New Syllabus

iGCSE Chemistry MCQ (Extended) Paper 2 - All Chapters

Question

Which diagram shows the outer shell electron arrangement for a molecule of methanol, \(\mathrm{CH_3OH}\)?

▶️ Answer/Explanation
In methanol (\(\mathrm{CH_3OH}\)), the carbon atom forms four single covalent bonds (three with hydrogen atoms and one with the oxygen atom). The oxygen atom forms two single covalent bonds (one with carbon and one with hydrogen) and has two lone pairs of electrons. All atoms achieve noble gas electronic configurations. Diagram (A) correctly shows this arrangement.
✅ Answer: (A)

Question

Which dot-and-cross diagram shows the outer shell electron arrangement in a molecule of nitrogen?

▶️ Answer/Explanation
A nitrogen atom has 5 outer electrons. In a nitrogen molecule (N₂), the two nitrogen atoms share three pairs of electrons to form a triple covalent bond. This results in each nitrogen atom having one lone pair and three shared pairs, making a total of 8 electrons in its outer shell. The correct dot-and-cross diagram must show this triple bond with the remaining two electrons on each atom as a lone pair.
✅ Answer: (B)

Question

Methanal, \(CH_2O\), has a boiling point of –19 °C. At –20 °C, the liquid methanal is a non-conductor of electricity. In a sample of methanal, each atom of carbon, hydrogen and oxygen has noble gas electronic configuration. Each atom has achieved this electronic configuration in one of three ways:
• gaining electrons
• losing electrons
• sharing electrons.
Which statement describes the bonding between the carbon atom and the oxygen atom in methanal?
A. The carbon atom and the oxygen atom share four electrons.
B. The carbon atom and the oxygen atom share two electrons.
C. Carbon is a negative ion and oxygen is a positive ion. These two ions attract each other.
D. Carbon is a positive ion and oxygen is a negative ion. These two ions attract each other.

▶️ Answer/Explanation
Methanal (formaldehyde) is a covalent molecule; it does not conduct electricity as a liquid, which rules out ionic bonding (options C and D). The carbon atom forms a double covalent bond with the oxygen atom (one sigma bond and one pi bond). A double bond involves sharing four electrons (two pairs). The remaining two bonds from carbon are to hydrogen atoms (single bonds). Therefore, option A is correct and B is incorrect because two shared electrons would indicate a single bond, not the actual carbon–oxygen double bond present in methanal.
✅ Answer: (A)
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