CIE iGCSE Co-Ordinated Science C2.5 Simple molecules and covalent bonds Exam Style Questions Paper 2
▶️ Answer/Explanation
Nitrogen (N₂) has a triple covalent bond, with three shared pairs of electrons between the two nitrogen atoms. Ethene (C₂H₄) has a double covalent bond between the two carbon atoms, with each carbon also forming single bonds to two hydrogen atoms. In the correct dot-and-cross diagram (Option A), nitrogen shows three shared pairs, and ethene shows the double bond between carbons and single bonds to hydrogens, with appropriate electron dots and crosses.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Simple covalent molecules have no free electrons or ions in any state, so they do not conduct electricity — low electrical conductivity is a defining property of all simple covalent compounds.
They typically have low melting points (not high), are often volatile (not low volatility), and are generally not soluble in water (unless they can form hydrogen bonds or ionise); so the only universally correct property is low electrical conductivity.
✅ Answer: (A)
They typically have low melting points (not high), are often volatile (not low volatility), and are generally not soluble in water (unless they can form hydrogen bonds or ionise); so the only universally correct property is low electrical conductivity.
✅ Answer: (A)
▶️ Answer/Explanation
Carbon dioxide (CO₂) has two double covalent bonds. Each oxygen shares two pairs of electrons with carbon. The correct diagram shows carbon sharing two electron pairs with each oxygen, forming O=C=O.
✅ Answer: (A)
✅ Answer: (A)
Question
What is a property of a typical covalent compound?
(A) low electrical conductivity
(B) high melting point
(C) low volatility
(D) soluble in water
▶️Answer/Explanation
Ans: A
Question
Which dot-and-cross diagram represents the outer-shell electrons in a molecule of methanol?
▶️Answer/Explanation
Ans : A