Atoms interact to form chemical bonds, holding them together in molecules and compounds. One pervasive type is the covalent bond, characterized by the sharing of electrons between atoms. This sharing allows atoms to achieve greater stability. This article explores how nonpolar covalent bonds are formed.
The Core of Covalent Bonding
Atoms form chemical bonds to achieve a stable electron configuration, often by attaining a full outer electron shell, mimicking noble gases. In covalent bonding, atoms satisfy this desire by sharing valence electrons, creating a strong attractive force.
The shared electron pair is attracted to the nuclei of both participating atoms. This allows each atom to count the shared electrons towards its outer shell, satisfying its need for a stable electron count. This principle underpins all covalent bond formation, regardless of whether the sharing is equal or unequal.
Electronegativity’s Role
The concept of electronegativity is central to understanding covalent bonds and how electrons are distributed. Electronegativity describes an atom’s ability to attract shared electrons within a chemical bond. This property is quantified using scales like the Pauling scale, where values range from approximately 0.7 for francium to 3.98 for fluorine, the most electronegative element.
Electronegativity is influenced by factors such as the number of protons in the nucleus and the distance of valence electrons from the nucleus. Atoms with a higher nuclear charge and smaller atomic radii exhibit greater electronegativity because their nuclei exert a stronger pull. Imagine it as a tug-of-war for the electron pair. The strength of each atom in this tug-of-war is its electronegativity. The difference in electronegativity values between two bonded atoms dictates how equally or unequally electrons are shared.
The Equal Sharing Mechanism
Nonpolar covalent bonds form when electrons are shared equally between two atoms. This equal distribution of electron density occurs when the two bonded atoms have either identical or very similar electronegativity values. When the electronegativity difference is zero, as with identical atoms, the electron pair is shared symmetrically, residing midway between nuclei. For example, in a hydrogen molecule (H₂), the electronegativity difference is 0.0.
Even when atoms are not identical, a nonpolar covalent bond can form if their electronegativity difference is very small. A difference of 0.4 or less on the Pauling scale indicates a nonpolar covalent bond. In such instances, neither atom has a significantly stronger pull on the shared electrons than the other. This balanced sharing results in the electron cloud being distributed evenly around both nuclei, preventing any buildup of partial positive or negative charges.
The absence of partial charges is a defining characteristic of nonpolar bonds. The electron density is uniformly spread, meaning no distinct positive or negative poles exist across the bond, and no dipole moment is created. This uniform distribution distinguishes nonpolar bonds from polar covalent bonds, where unequal sharing creates slight charge separations. This symmetrical electron distribution ensures the shared electrons spend an equal amount of time around each nucleus.
Everyday Nonpolar Examples
Nonpolar covalent bonds are found in many molecules, especially those composed of identical atoms. Diatomic elements like hydrogen (H₂), oxygen (O₂), nitrogen (N₂), and chlorine (Cl₂) are classic examples. In these molecules, two atoms of the same element bond, resulting in a precisely zero electronegativity difference and perfectly equal electron sharing. For instance, the nitrogen molecule (N₂) features a triple bond where six electrons are equally shared.
Nonpolar bonds also exist in molecules where different elements bond, but their electronegativity difference is minimal. A prime example is the carbon-hydrogen (C-H) bond found extensively in hydrocarbons like methane (CH₄) and octane. Carbon (2.55) and hydrogen (2.20) have a difference of 0.35, which falls within the nonpolar range, making C-H bonds essentially nonpolar.
The overall nonpolar nature of molecules containing these bonds often dictates their physical properties. For example, molecules like oils and fats, primarily held together by nonpolar covalent bonds, do not dissolve well in water. Water is a highly polar molecule, and the principle of “like dissolves like” explains why nonpolar substances mix poorly with polar solvents.