What is The Bond Angle of a Molecule?
Table of Contents
The bond angle is the average angle between the orbitals in a molecule containing bonding electron pairs.
Definition
The bond angle is the angle between two bonds that share a common atom.
It is also defined as
The angle forms between two orbitals containing bonding electron pairs surrounding the central atom in a molecule or ion.
Example
Unit:
It is denoted by a degree ( ° )
Value:
Its Values is ranges from 0°to 180°
Explanation
It can be defined as a geometric angle between two adjacent covalent bonds. It is used as a parameter to determine the geometry of a molecule. It is measured in degrees. It can be calculated by using the spectroscopic method. It provides information about the distribution of bonded electron pairs around the atoms. It determines the shape of the molecules. Its value is between 0° to 180°.
Factors Affect the Bond Angle
Three factors affect its value
It mainly depends upon the following three factors.
- Hybridization
- Lone pair repulsion
- Electronegativity
Hybridization
The hybridization of the central atom determines the bond angle of a molecule of a compound. There are three types of hybridization.
The type with a greater “S” character has a larger value of the bond angle.
| Hybridization | “S” character | Bond angle |
| sp3 | 25% | 109.28o |
| sp2 | 33% | 120° |
| Sp | 50% | 180o |
Lone Pair Repulsion
Lone pair is a type of electron pair that does not participate in forming a bond. The lone pair of electrons is the central atom, which affects the angle between the orbitals. According to VSEPR theory, a lone pair repels other electron pairs far apart. Thus, decreasing its value.
- CH4 (having no lone pair) = 109.28o
- NH3 (having one lone pair) is = 107°
- H2O (having two lone pairs) is = 104.5o
Electronegativity
Its values directly vary with the electronegativity of the central atom.
If the electronegativity value decreases for the central atom, its value will decrease. For example, the NH3 bond angle is 107°, while its value for PH3 is 93.5°.
The other case is for the electronegativity of substituent atoms.
It inversely varies with the electronegativity of the substituent atoms.
If the electronegativity value decreases for the substituent atoms, it will increase. For example
NH3 has a value of 107°, while its value for NF3 is 102.3°.
Relationships Between Bond Angle and Bond Length
It has an inverse relationship with bond length.
The larger its value, the shorter will be the bond length.
Bond angles Table:
Below is the given table for the bond angle values of some important compounds in relation to geometry.
Conclusion
- The bond angle is the angle between the orbitals of a molecule.
- It can be determined by the mutual repulsion of electron pairs, the electronegativity of a central atom or substituent atoms, and by hybridization of a molecule.
- It varies inversely with bond length.
FAQ’S
Does polarity affect bond angle?
Yes, polarity affects its value. Due to polarity, electronic density is greater at the central or substituent position. Thus, the bond angle changes.
Does electronegativity affect bond angles?
It is inversely proportional to the electronegativity of the substituents. And directly proportional to the central atom. A more electronegative substituent attracts the electrons towards itself, thus decreasing the charge density on the central atom. This results in a decrease in its value.
Why are some bond angles smaller than others?
It is due to lone pair of electrons. Lone pair of electrons requires more space than a bond pair of electrons. This affects the molecular geometry. As a result, they are smaller than those of the ideal geometry.
Why does the CH4 molecule have a 109.5o?
In methane (CH4), the central atom is Carbon. The hybridization of Carbon is SP3. The molecule with SP3 hybridization has a 109.5o. It has four H-atoms situated at the four corners of the tetrahedron. It’s between H—C—H is 109.5°, called the tetrahedral angle.
