Bromine is a highly toxic diatomic liquid compound represented by the chemical formula Br2. It exists as a volatile brownish-red liquid with a sharp odour at room temperature.
Bromine is the only element other than mercury in the liquid state at standard temperature and pressure. The name bromine comes from the Greek word “Bromos”, which means stench (unpleasant smelling).
This article will discuss a very important property of bromine (Br2), i.e., its polarity. So, is Br2 polar or non-polar? Continue reading to find out.
Is Br2 polar or non-polar?
Bromine (Br2) is a non-polar molecule. The Br-Br bond in the Br2 molecule is non-polar due to no electronegativity difference between the bonded atoms.
As the Br2 molecule contains two same atoms and there is no difference in electronegativity between the two atoms, the electronic charge is evenly distributed over the molecule.
Due to this, the Br-Br bond in the Br2 molecule is non-polar and possesses no dipole moment value.
Thus, the symmetric, linear Br2 molecule is non-polar with a net dipole moment equal to 0.
A molecule with an equal charge distribution between different centers of bonded atoms is a non-polar molecule.
It is formed by the covalent bond between two same atoms leading to a symmetric electron density in the molecule, such as the Br2 molecule.
In the case of asymmetric molecules, If the dipole moments of individually polar bonds are canceled, the molecule will be non-polar.
Hence, a non-polar molecule has an equal distribution of the electronic charge. Contrarily, if the electronic charge is not evenly distributed over the molecule, in that case, it will be a polar molecule.
The following three factors influence the polarity of any covalent molecule:
Electronegativity.
Dipole moment.
Molecular geometry or shape.
In the next section, we will uncover how these factors lead to the non-polar nature of the bromine (Br2) molecule. Continue reading.
Factors affecting the polarity of Br2
Electronegativity
It is defined as the ability of an atom to attract a shared pair of electrons from a covalent chemical bond.
Electronegativity decreases down the group in the Periodic Table of elements while it increases across a period.
It is directly related to the polarity of any molecule. The greater the difference in electronegativity between atoms in a molecule, the higher will be the bond polarity.
Bromine belongs to group VII-A (or 17) of the Periodic Table. The electronic configuration of bromine is [Ar]3d104s24p5, so it has 7 valence electrons for bonding.
Thus, the two Br atoms form a single covalent bond to complete their octet configuration in the Br2 molecule.
One valence electron consumed in bonding out of the seven initially available leaves behind six valence electrons, i.e., three lone pairs of electrons on each Br atom in the Br2 molecule.
Atom
Electronic configuration
Valence electrons
Bromine (35Br)
1s22s22p63s23d104s24p5
7
According to Pauling’s electronegativity scale, a molecule is non-polar if there is an electronegativity difference of 0 units between the bonded atoms.
The electronegativity of the bromine atom is 2.96 on Pauling’s scale. There is no difference in electronegativity between the same bonded atoms in the Br2 molecule.
Due to the zero electronegativity difference, there is a uniform electronic charge distribution in the Br2 molecule overall. As a result, no charged poles are developed in the Br2 molecule.
Thus, the Br-Br bond is non-polar in Br2 molecule.
Dipole Moment
The dipole moment is the product of electrical charge (Q) and bond length (r) between two bonded atoms. It is a vector quantity expressed in Debye (D) units.
It is represented by a Greek symbol µ and measures the polarity of a bond.
The dipole moment of any molecule depends on the difference in electronegativity between the bonded atoms. The greater the electronegativity difference, the higher the bond polarity, resulting in a high dipole moment value.
It points from the partial positive (δ+) center to the partial negative (δ–) center of a bond or molecule.
As the Br2 molecule constituents the atoms of the same element (Br), there is no difference in electronegativity between the bonded atoms. Due to this, the net dipole of the Br-Br bond is zero in the Br2 molecule.
As a result of the zero dipole moment of the Br-Br bond, the Br2 molecule is non-polar.
Molecular geometry
As discussed earlier, a bromine (Br2) molecule consists of a single Br-Br covalent bond. The overall molecule consists of a total of 14 valence electrons. There are three lone pairs of electrons on each Br atom.
The molecule adopts a linear shape to minimize the repulsion effects due to the lone pairs on each Br atom. There is a bond angle of 180 degrees.
Due to no electronegativity difference between the bonded atoms, the only Br-Br bond has no dipole moment value in the bromine (Br2) molecule. There is an equal charge distribution over the molecule.
Thus, bromine (Br2) is a non-polar molecule with a zero dipole moment.
Difference between polar and nonpolar?
Polar molecule
Non-polar molecule
Atoms must have a difference in electronegativity
Atoms may have the same or different electronegativity values
Unequal charge distribution overall
Equal charge distribution overall
Net dipole moment greater than zero
Net dipole moment equals to zero
Examples include water (H2O), ethanol (CH3CH2OH), ammonia (NH3), sulfur dioxide (SO2), bromine trifluoride (BrF3), nitric oxide (NO), bromine pentafluoride (BrF5), etc.
Examples include oxygen (O2), nitrogen (N2), fluorine (F2), bromine (Br2), methane (CH4), sulfur trioxide (SO3), etc.
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