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# Massachusetts Comprehensive Assessment System

## 2011, High School Chemistry

Question 45: Open-Response
Carbon forms covalent bonds with many different elements.
1. Describe the difference between a nonpolar covalent bond and a polar covalent bond.
2. Using electronegativity trends in the periodic table, rank the three covalent bonds shown below in order from least polar to most polar. Explain your reasoning.
 C–N C–C C–O
1. Identify one covalent bond from part (b) in which the carbon atom has a partial positive charge. Explain your answer.

### Scoring Guide and Sample Student WorkSelect a score point in the table below to view the sample student response.

ScoreDescription
4 The response demonstrates a thorough understanding of using electronegativity to explain the difference between polar and nonpolar covalent bonds. The response clearly describes the difference between a nonpolar covalent bond and a polar covalent bond. The response correctly ranks the three given covalent bonds in order from least polar to most polar and uses electronegativity trends in the periodic table to explain the reasoning. The response also correctly identifies a covalent bond in part (b) in which the carbon atom has a partial positive charge and clearly explains the answer.
4
3
The response demonstrates a general understanding of using electronegativity to explain the difference between polar and nonpolar covalent bonds.
2
The response demonstrates a limited understanding of using electronegativity to explain the difference between polar and nonpolar covalent bonds.
1
The response demonstrates a minimal understanding of using electronegativity to explain the difference between polar and nonpolar covalent bonds.
0
The response is incorrect or contains some correct work that is irrelevant to the skill or concept being measured.

Note: There are 2 sample student responses for Score Point 4.

Question 11:
Question 23:
Question 33:
Question 44:
Question 45: