Intramolecular Force and Potential Energy
Introduced| English |
|---|
| potential energy/pəˈtenʃl ˈenədʒi/ |
| bond length/bɒnd leŋθ/ |
| bond energy/bɒnd ˈenədʒi/ |
The perfect distance apart
- Push two bonded atoms too close and they shove back.
- Pull them too far and they snap toward each other.
- Somewhere between sits a comfortable resting gap.
- A single curve captures this tug-of-war.
The bond's energy curve
- Plot the potential energy 势能 against the distance between two atoms.
- Far apart it is near zero; too close it shoots up from repulsion.
- The lowest point is the stable bond length 键长.
On a potential-energy versus distance curve, the bond length is at the...
The minimum is the stable separation -- the bond length.
Depth means strength
- The depth of the well is the bond energy 键能, the energy to break the bond.
- A deeper well means a stronger bond.
- Breaking a bond costs energy; forming one releases it.
A deeper potential-energy well means a stronger bond.
The well depth is the bond energy needed to break the bond.
Breaking a chemical bond...
You must supply energy to pull bonded atoms apart.
Forming a bond releases energy.
Bond formation is exothermic -- the reverse of breaking.
Shorter bonds, stronger bonds
- More shared pairs (a higher bond order) pull the atoms closer.
- A double bond is shorter and stronger than a single bond.
- So bond length and bond strength move in opposite directions.
Compared with a single bond, a double bond between the same atoms is...
More shared pairs pull the atoms closer and hold them more tightly.
As bond order rises, bond length gets shorter and bond strength gets ____.
Shorter bonds are stronger, so strength increases as length decreases.
Compare a C--C single bond with a C=C double bond.
- The double bond has more shared electrons.
- It is shorter and needs more energy to break, so it is stronger.
Reading the potential-energy curve
As two atoms approach, their potential energy changes. Match each region of the curve to what the atoms are doing.
The bottom of the well is the natural bond length, where attraction and repulsion balance -- not where the energy is zero. Breaking a bond always requires energy (endothermic); forming one always releases it (exothermic). And a deeper well means a stronger and shorter bond, all together.
A bond's potential energy curve dips to a minimum at the bond length, where attraction and repulsion balance. The depth of that well is the bond energy needed to break the bond. More shared pairs pull atoms closer, so higher-order bonds are both shorter and stronger.