3 marksShort AnswerSection Section B

Consider the following organic compounds :

(i) $H-C(H)(H)-C(H)(H)-C(H)=O$

(ii) $H-C(H)(H)-C(H)=O

(a) Name the functional group present in their compounds.

(b) Write the general formula for the compounds of this functional group.

(c) State the relationship between these compounds and draw the structure of any other compound having similar functional group.

Q: Consider the following organic compounds : (i) $H-C(H)(H)-C(H)(H)-C(H)=O$ (ii) $H-C(H)(H)-C(H)=O (a) Name the functional group present in their compounds. (b) Write the general formula for the compounds of this functional group. (c) State the relationship between these compounds and draw the structure of any other compound having similar functional group.

(a) **Electron dot structure for ethyne ($C_2H_2$):** In ethyne, there is a triple covalent bond between the two carbon atoms and a single covalent bond between each carbon and hydrogen atom. $$\text{H} \bullet \times \text{C} \begin{matrix} \bullet \times \\ \bullet \times \\ \bullet \times \end{matrix} \text{C} \times \bullet \text{H}$$ ```molecule {"smiles": "C#C", "caption": "Ethyne (C2H2)"} ``` (b) **Differences between covalent and ionic compounds:** | Property | Covalent Compounds | Ionic Compounds | | :--- | :--- | :--- | | **Melting & Boiling Points** | Have low melting and boiling points because the intermolecular forces of attraction are weak. | Have high melting and boiling points due to strong electrostatic forces of attraction between oppositely charged ions. | | **Electrical Conductivity** | Generally poor conductors of electricity because they do not form any ions (electrons are shared). | Conduct electricity in molten state or in aqueous solution because ions are free to move. |

Carbon and its Compounds

Bonding in Carbon - The Covalent Bond

Official Answer

(a) Electron dot structure for ethyne ( $C_2H_2$ ):

In ethyne, there is a triple covalent bond between the two carbon atoms and a single covalent bond between each carbon and hydrogen atom.

$\text{H} \bullet \times \text{C} \begin{matrix} \bullet \times \\ \bullet \times \\ \bullet \times \end{matrix} \text{C} \times \bullet \text{H}$

Ethyne (C2H2)

(b) Differences between covalent and ionic compounds:

Property	Covalent Compounds	Ionic Compounds
Melting & Boiling Points	Have low melting and boiling points because the intermolecular forces of attraction are weak.	Have high melting and boiling points due to strong electrostatic forces of attraction between oppositely charged ions.
Electrical Conductivity	Generally poor conductors of electricity because they do not form any ions (electrons are shared).	Conduct electricity in molten state or in aqueous solution because ions are free to move.

ethynetriple bondshared pairslow melting pointhigh melting pointpoor conductorsconduct electricityions

Marking Scheme

11.5 Marks for drawing a correct and clear electron dot structure of ethyne showing the triple bond and C-H single bonds.
21.5 Marks for listing two correct differences between covalent and ionic compounds (0.75 marks per difference).

Hint

Ethyne has a triple bond between the carbons. For the differences, think about why salt (ionic) melts at a much higher temperature than sugar (covalent) and which one conducts electricity.

Quick Oral Answer

Q: How many covalent bonds are there in a molecule of ethyne? A: There are 5 covalent bonds in total: 1 triple bond between the carbon atoms (which counts as 3 bonds) and 2 single C-H bonds.

Analysis & Explanation

Ethyne ( $C_2H_2$ ) is an alkyne containing a triple bond. The electron dot structure must clearly show 6 shared electrons between the two carbon atoms and 2 shared electrons between each carbon-hydrogen pair. The comparison of physical properties highlights how microscopic bonding (ions vs. neutral molecules) dictates macroscopic properties (melting point, conductivity).

Common Mistakes

1Drawing a double bond instead of a triple bond for ethyne (confusing it with ethene).
2Forgetting to show the sharing of electrons clearly in the dot structure.
3Stating that covalent compounds conduct electricity in solid state.

Interesting Facts

Ethyne is commonly known as acetylene and is used in oxy-acetylene welding because its combustion with oxygen produces an extremely hot flame of over $3000^\circ\text{C}$ .

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2022?

This question carries 3 marks in the CBSE Class 10 Science 2022 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Carbon and its Compounds" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Bonding in Carbon - The Covalent Bond" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2022 paper?

This is a Short Answer question from Section Section B in the CBSE Class 10 Science 2022 paper.