Bond Parameters
Length, Angle, Enthalpy & Order | Chemical Bonding
1. Bond Length
The equilibrium distance between the nuclei of two bonded atoms in a molecule.
Factors Affecting Bond Length:
- Size of Atoms: Larger size $\rightarrow$ Longer bond ($H-I > H-Br > H-Cl > H-F$).
- Multiplicity: Triple bond < Double bond < Single bond ($C\equiv C < C=C < C-C$).
- Hybridization: More s-character $\rightarrow$ Shorter bond ($sp < sp^2 < sp^3$).
2. Bond Angle
The angle between the orbitals containing bonding electron pairs around the central atom.
Factors Affecting Bond Angle:
- Hybridization: $sp (180^\circ) > sp^2 (120^\circ) > sp^3 (109.5^\circ)$.
- Lone Pairs: Repulsion ($lp-lp > lp-bp > bp-bp$) reduces bond angles. ($CH_4 [109.5^\circ] > NH_3 [107^\circ] > H_2O [104.5^\circ]$).
- Electronegativity: If central atom is more electronegative, bond angle increases. If surrounding atom is more electronegative, bond angle decreases.
3. Bond Enthalpy (Bond Energy)
The amount of energy required to break one mole of bonds of a particular type between two atoms in a gaseous state.
- Bond Strength: Higher enthalpy means a stronger bond.
- Anomaly: Expected $F-F > Cl-Cl$. Actual $Cl-Cl > F-F$.
Reason: High inter-electronic repulsion in small F atom weakens the $F-F$ bond.
4. The Master Relationship
Understanding this single relationship solves 80% of bonding questions:
$$ \text{Bond Order} \propto \text{Bond Strength/Enthalpy} \propto \text{Stability} \propto \frac{1}{\text{Bond Length}} $$
Bond Order: The number of bonds between two atoms (1 for single, 2 for double, 3 for triple).
Example: In $N_2$ (Order 3), bond is shortest and strongest. In $F_2$ (Order 1), bond is longer and weaker.
5. Comparative Summary
| Parameter | Single Bond ($C-C$) | Double Bond ($C=C$) | Triple Bond ($C\equiv C$) |
|---|---|---|---|
| Bond Length | 154 pm | 134 pm | 120 pm |
| Hybridization | $sp^3$ | $sp^2$ | $sp$ |
| % s-character | 25% | 33.3% | 50% |
Practice Quiz
Test your knowledge on Bond Parameters.
Very nice explanation. Good work
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