Nitrogen gas (\(\text{N}_2\)) is the most abundant component of Earth’s atmosphere, making up approximately 78% of the air we breathe. Despite the strong triple bond holding its two atoms together, \(\text{N}_2\) is classified as a nonpolar molecule. This nonpolar nature is a direct consequence of both the specific atoms involved and the molecule’s simple, symmetrical structure.
Defining Molecular Polarity
Molecular polarity describes an uneven distribution of electrical charge across a molecule. This charge separation occurs when atoms within a molecule share electrons unequally in their covalent bonds. Unequal sharing leads to one atom acquiring a slight negative charge (delta minus) and the other atom developing a corresponding slight positive charge (delta plus). This resulting separation of charge creates a dipole moment. A molecule is considered polar if this charge separation is permanent and does not cancel out due to the molecule’s shape.
The Role of Electronegativity in \(\text{N}_2\)
Electronegativity is an atom’s inherent power to attract a shared pair of electrons toward itself. The \(\text{N}_2\) molecule is a diatomic species, composed of two identical nitrogen atoms. Because the atoms are the same, they possess the exact same electronegativity value. When they form a triple covalent bond, they pull on the shared electrons with precisely equal force, ensuring the electron cloud is distributed uniformly. This perfect balance results in a zero difference in electronegativity, meaning the bond itself is nonpolar and is the primary reason for the molecule’s overall lack of polarity.
Symmetry and the Absence of a Net Dipole
While the bond itself is nonpolar due to the equal pull, a molecule’s overall polarity is also governed by its three-dimensional shape. For a molecule to be nonpolar, it must either contain nonpolar bonds, as is the case with \(\text{N}_2\), or its structural symmetry must cause any individual bond dipoles to perfectly cancel each other out. The \(\text{N}_2\) molecule is linear because it only contains two atoms bonded together. This simple, linear structure is inherently symmetrical, reinforcing the nonpolar nature established by the identical atoms. Because the electrons are shared equally and the charge distribution is uniform, the entire \(\text{N}_2\) molecule has a net dipole moment of zero, meaning it only interacts through very weak London dispersion forces.