Covalent compounds have low melting and boiling point. Why?
Covalent compounds have low melting and boiling point. Why?
Official answer
Covalent compounds have low melting and boiling points because the intermolecular forces of attraction between the molecules are very weak. Although the covalent bonds within the molecules themselves (intramolecular bonds) are strong, only a small amount of thermal energy is required to break the weak forces holding the separate molecules together.
Marking scheme
- 1.Mentioning that intermolecular forces of attraction between molecules are weak. (0.5 marks)
- 2.Explaining that less energy is required to overcome these weak forces, leading to low melting and boiling points. (0.5 marks)
Hint
Think about the difference between the forces holding atoms together inside a molecule versus the forces holding different molecules to each other.
Quick oral answer
Covalent compounds have low melting and boiling points because the forces of attraction between their molecules, known as intermolecular forces, are very weak. Thus, very little heat energy is needed to separate the molecules from one another.
Common mistakes
- 1.Confusing intermolecular forces with intramolecular covalent bonds, leading to the incorrect belief that covalent bonds themselves are weak.
- 2.Stating that covalent compounds conduct electricity when they melt, which is incorrect because no ions are formed.
Analysis and explanation
In covalent compounds, atoms share electrons to achieve a stable noble gas configuration. This sharing forms strong bonds within each individual molecule. However, the forces acting between different molecules (intermolecular forces, such as van der Waals forces) are weak. When a covalent substance melts or boils, it is these weak intermolecular forces that are overcome, not the strong covalent bonds within the molecules. Hence, very little heat energy is needed, resulting in low melting and boiling points.
Interesting facts
While most molecular covalent compounds have low melting points, network covalent solids like diamond have extremely high melting points because you must break strong covalent bonds throughout the entire 3D lattice to melt them.
Question details
Q1 of 45 questions
- Board
- CBSE
- Class
- Class 10
- Subject
- Science
- Year
- 2020
- Section
- Section A
- Marks
- 1
- Type
- Very Short Answer
- Chapter
- Carbon and its Compounds
- Topic
- Bonding in Carbon – The Covalent Bond
- Bloom's level
- Understanding
- Syllabus topic
- Covalent bonding in carbon compounds. Versatile nature of carbon.
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Frequently asked questions
How many marks does this question carry in CBSE Class 10 Science 2020?
This question carries 1 mark in the CBSE Class 10 Science 2020 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 2020 paper?
This is a Very Short Answer question from Section A in the CBSE Class 10 Science 2020 paper.