The chlorine molecule, represented by the chemical formula \(\text{Cl}_2\), is a nonpolar molecule. This classification means the molecule has an even distribution of electrical charge across its structure, leading to no net separation of positive and negative regions. Understanding why chlorine behaves this way requires examining how its two constituent atoms share electrons and considering the overall symmetry of the molecule.
Defining Polarity and Nonpolarity
Molecular polarity is a measure of the charge separation within a molecule, which results in an electrical dipole moment. A polar molecule possesses a partial positive charge on one end and a partial negative charge on the opposite end because the shared electrons spend more time near one atom than the other. This unequal sharing creates a net dipole. The presence of these separated charges influences the molecule’s physical properties, such as its solubility and boiling point.
In contrast, a nonpolar molecule features an equal or near-equal distribution of its electron cloud. This equal sharing means there is no significant difference in charge across the molecule, leading to a zero or negligible net dipole moment. Nonpolarity can arise either from the perfect equality of electron sharing in the bond itself or from a perfectly symmetrical molecular shape where any existing partial charges cancel each other out.
Electronegativity and Chemical Bonds
The underlying factor that dictates whether electrons are shared equally or unequally is a property called electronegativity. Electronegativity is an atom’s inherent power to attract a pair of shared electrons towards itself when forming a chemical bond. Atoms with higher electronegativity values exert a stronger pull on the shared electrons. The Pauling scale is commonly used to assign numerical values for this attraction, ranging from approximately 0.7 to 4.0.
The type of chemical bond formed between two atoms depends on the difference in their electronegativity values (\(\Delta\text{EN}\)). If the difference is very large, the bond is considered ionic, involving a complete transfer of electrons. If the difference is moderate, the bond is polar covalent, where electrons are shared but pulled more strongly toward the atom with higher electronegativity. A zero or near-zero difference in electronegativity results in a nonpolar covalent bond, where the electrons are shared equally between the two atoms.
The Polarity of the Chlorine Molecule
Applying these principles to the \(\text{Cl}_2\) molecule reveals its nonpolar nature. The molecule is composed of two identical chlorine atoms bonded together, known as a diatomic molecule. Because both atoms are chlorine, they possess the exact same electronegativity value (approximately 3.16 on the Pauling scale).
The difference in electronegativity (\(\Delta\text{EN}\)) between the two bonded chlorine atoms is zero (\(3.16 – 3.16 = 0\)). This zero difference ensures that the electron pair forming the chemical bond is shared equally between the two nuclei. Since neither atom can exert a greater pull on the shared electrons, there is no separation of charge, meaning the \(\text{Cl}-\text{Cl}\) bond itself is nonpolar.
The \(\text{Cl}_2\) molecule also has a linear geometry, which is perfectly symmetrical. This symmetrical arrangement prevents the formation of a net dipole moment. The combination of a nonpolar bond and a symmetrical structure confirms that chlorine (\(\text{Cl}_2\)) is a nonpolar molecule.