Nitrogen, ammonia and oxides of nitrogen
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 2 practice questions, 5 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Safe to breathe, but not to burn
- Why nitrogen is unreactive
Read the transcript of the teaching part
Last time
Before we start: last time, in Group 17, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Safe to breathe, but not to burn
The air is four fifths nitrogen, and we breathe it all day without harm. Yet in a car engine, a little of that nitrogen turns into oxides that cause smog and acid rain. The same element is both inert and, under the right conditions, the source of fertiliser, explosives and pollution.
Why nitrogen is unreactive
A nitrogen molecule has a triple bond: one sigma and two pi bonds. The bond energy is 944 kilojoules per mole. A very large amount of energy is needed to break this bond, so reactions have a high activation energy. The molecule is also non-polar, so it does not attract polar reagents. A pi bond forms by sideways overlap of two p orbitals, one on each nitrogen atom, giving electron density above and below the axis.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Ammonia and the ammonium ion · Oxides of nitrogen and air pollution.
The whole chapter: Nitrogen and Sulfur, Nitrogen and Sulfur.
Chapter 12: Nitrogen and sulfur
- Nitrogen, ammonia and oxides of nitrogen 7 min
Also for A Level Chemistry 9701
Which topics come up most in A Level Chemistry 9701 past papers, counted from every paper since 2004: Paper 2 topic frequency, Paper 4 topic frequency.