AQA A-Level Chemistry Paper 3, 2021: Question 16
1 mark · Easy difficulty · Multiple Choice
This question tests your understanding of molecular polarity. You are asked to identify which molecule has a permanent dipole, which depends on both electronegativity differences and molecular shape.
Practise this questionQuestion
Question text
16 Which molecule has a permanent dipole?
[1 mark]
A BF3
B NH3
C SiCl4
D SO3
Mark scheme
Show the mark scheme
16 B 1 NH3
How to answer it
Permanent Dipole Question Explained
Correct Answer: B – NH3
NH3 is a polar molecule with a trigonal pyramidal shape due to a lone pair on nitrogen. The molecule is asymmetrical, so the dipoles don't cancel, and it has a permanent dipole.
Why the other answers are wrong:
A – BF3
Although B–F bonds are polar, BF3 has a symmetrical trigonal planar shape. The dipoles cancel out, so there is no permanent dipole.
Although B–F bonds are polar, BF3 has a symmetrical trigonal planar shape. The dipoles cancel out, so there is no permanent dipole.
C – SiCl4
Tetrahedral and symmetrical. Although Si–Cl bonds are polar, the symmetry of the molecule causes the dipoles to cancel out.
Tetrahedral and symmetrical. Although Si–Cl bonds are polar, the symmetry of the molecule causes the dipoles to cancel out.
D – SO3
Trigonal planar and symmetrical. Even though S–O bonds are polar, the molecule has no overall dipole because of its shape.
Trigonal planar and symmetrical. Even though S–O bonds are polar, the molecule has no overall dipole because of its shape.
Topics
Physical Chemistry · 3.1.3 Bonding
Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.