Bond Energy and Length
Stronger bonds are shorter and need more energy to break.
About this topic
Bond length is the distance between two bonded nuclei, and bond energy is the energy required to break one mole of bonds in the gas phase. Triple bonds are shorter and stronger than double bonds, which are shorter and stronger than single bonds: C–C is about 348 kJ/mol, C=C 614 and C≡C 839.
Bond length arises from a balance between attraction of nuclei for the shared electrons and repulsion between the nuclei. More shared pairs pull the atoms closer, and smaller atoms form shorter bonds. Breaking bonds absorbs energy (endothermic), while forming bonds releases energy (exothermic). The overall enthalpy change of a reaction can be estimated as energy of bonds broken minus energy of bonds formed.
Example: in burning methane, you break four C–H and two O=O bonds, then form two C=O and four O–H bonds. Because the new bonds are stronger in total, the reaction releases energy. Nitrogen's triple bond, at 945 kJ/mol, makes N2 very stable, which is why nitrogen fertiliser is hard to make.
Students often think breaking bonds releases energy; it always takes energy in. Also, bond energies are averages and give only approximate results. Longer bonds are generally weaker and more reactive.
Key ideas
- Triple > double > single
- Measured in kJ/mol
- Reactions break and form bonds
Quick check
Use cases: where Bond Energy and Length helps
- Homework: review the key idea behind Bond Energy and Length before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Bond Energy and Length without notes.
- Visual learning: play with the interactive lab to see how Bond Energy and Length changes when you adjust its inputs.
- Teaching a friend: explain Bond Energy and Length in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Bond Energy and Length?
Stronger bonds are shorter and need more energy to break.
What will I learn in Bond Energy and Length?
Triple > double > single. Measured in kJ/mol. Reactions break and form bonds.
Is Bond Energy and Length part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Bond Energy and Length lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Bond Energy and Length?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.