The bond pair and lone pair are the electrons pairs. The key difference between bond pair and lone pair is that bond pair is involved in bonding while lone pair is never. When chemical reactions take place between the molecules. Compounds are formed in which there are various bond pairs and lone pairs.
Difference between bond pair and lone pair
|Bond Pair||Lone Pair|
|It is attracted by two nuclei||it is attracted by only one nucleus|
|They are localized||They are more delocalized|
|B.P-B.P repulsion is less than L.P-L.P||L.P-L.P repulsion is greater than B.P-B.P|
|They occupy less space||They occupy more space|
|They are always in bonds||They are not in bonds but can be formed a bond by donating lone pair|
|When two atoms share their electrons result in a bond pair is formed||It is formed due to the absence of empty orbitals|
|A molecule having two bond pairs and no lone pair is linear||A molecule having two lone pairs and no bond pair is nonlinear|
These are pairs of electrons that are responsible for bonding. These electron pairs can be seen in covalent and coordination bonds. Where equal sharing of electrons takes place, the result of this a bond is formed. Sigma bond and pi bond are also composed of bond pairs.
For example, in methane, there are four hydrogen atoms are bonded with a carbon atom.
These electrons pair are not involved in bonding. They are also known as nonbonding electron pairs. Different compounds have a different number of lone pairs.
For example, such as water has two lone pairs, and ammonia has one lone pair.
Effect of lone pair and bond pair
There are three types of theories that explain their effect on the shapes and chemical or physical behaviors of molecules.
- Valance Bond Theory
- VSEPR Theory
- Molecular Orbital Theory
Valance Bond Theory (VBT)
This theory provides a simple description of the small inorganic molecules. It also explains the effect of lone and bond pairs on the molecules.
Postulates of VBT
- Atoms with unpaired electrons tend to combine with each other.
- When unpaired electrons are paired up. The atoms attain a stable electronic configuration usually like noble gases.
- The number of bonds formed by an atom is the same as the number of unpaired electrons in the ground state.
- A bond is formed by the pairing of electrons. The spin of two electrons must be opposite.
H = 1sl
H = 1sl
N = 1s2, 2s2,2p3
H = 1sl
H = 1sl
H = 1sl
O = 1s2,2s2,2p4
O = 1s2,2s2,2p4
According to VBT, oxygen is diamagnetic because there are no unpair electrons. It is paramagnetic according to the molecular orbital theory which is a drawback of VBT.
Drawbacks of valence bond theory
- The VBT can satisfactorily explain the bonding of simple molecules like Beryllium, Boron, and Carbon. According to VBT the formation of the covalent bond by an atom depends on the number of unpaired electrons in its valence shell.
Be = 1s2,2s2,2p
B = 1s2,2s2,2p1
C = 1s2,2s2,2p2
The atom is surrounded by pairs of electrons. These electrons are arranged in such a way that they are too far from each other to minimize the repulsive forces between them.
Postulates of VSEPR Theory
- The geometry of a molecule depends on the total number of electrons in the outermost shell.
- To reduce electron-electron repulsion and increase stability, the outermost shell electrons are far from each other.
- In the formation of a bond, the central atom shares its valence electrons with surrounding atoms.
- The most stable arrangement (if more than one geometrical arrangement is possible for the given number of bonded and non-bonded pairs) by the following rules
- The repulsion order is,
LP – LP > LP – BP > BP – BP
- Repulsive forces between electron pairs at vertices greater than 115o apart can be neglected.
Geometrical view of bond pair electrons
- Linear Triatomic (Angle 180o)
- Tetrahedral (Angle 109.5o)
- Trigonal bipyramidal (Angle 120o, 90o)
- Octahedral (Angle 90o, 90o)
- Pentagonal bipyramidal (Angles 72o, 90o)
Drawbacks of VSEPR Theory
- This theory was only applicable to covalently bonded compounds. It cannot be applicable to Ionic compounds.
- There was no distinction in s, p, d, f orbitals.
Molecular Orbital Theory
The molecular orbital theory explains how two atomic orbitals combine together. The result of the combination is the formation of the molecular orbitals. There are three types of molecular orbitals like bonding and antibonding and nonbonding molecular orbitals. Bonding and antibonding molecular orbitals have bond pairs while nonbonding orbitals have lone pairs.
Postulates of MOT
- The total number of molecular orbitals formed is equal to the total number of atomic orbitals.
- There are molecular orbitals formed such as bonding molecular orbitals, antibonding molecular orbitals, and nonbonding molecular orbitals.
- The antibonding molecular orbitals have high energy while bonding molecular orbitals have low energy.
- Electrons first fill the lowest energy orbitals (bonding molecular orbitals) and then high energy orbitals (antibonding molecular orbitals).
What is a bond pair?
These are electrons pair that are involved in bonding during chemical reactions. For example, when two atoms of hydrogen combine to give a hydrogen molecule. The bonding electrons between hydrogen atoms are known as bond pairs.
What is a lone pair?
Electrons pair that are not involved in bonding. For example, water molecules have two lone pairs.
Why does lone pair vs lone pair repulsion have a greater repulsive force than bonding pair vs bonding pair repulsion?
The lone pairs are more closer to the nucleus of atoms as compared to the bond pairs. That’s why lone pair to lone pair repulsion is greater than bond pair to bond pair.
What are lone pairs in chemistry?
In chemistry, those electrons pairs that do not take part in bonding during chemical reactions are called lone pairs.
What is the number of lone pairs in nitrogen?
There is only one lone pair in nitrogen. Which is not involved in bonding.
What is the number of lone pairs in oxygen?
There are two lone pairs in oxygen.