The way atoms connect to form molecules determines their physical and chemical nature. This process, known as chemical bonding, dictates how electrons are positioned between atoms. The chlorine molecule, represented as \(\text{Cl}_2\), is classified as a covalent molecule.
Understanding Chemical Bonds
Chemical bonds are categorized based on how valence electrons are handled between bonding partners. One major category is the ionic bond, which involves the complete transfer of one or more electrons, typically between a metal and a nonmetal atom.
The atom losing an electron becomes a positively charged ion (cation), while the atom gaining one becomes a negatively charged ion (anion). The resulting substance is held together by the strong electrostatic attraction between these oppositely charged ions. Ionic compounds, such as table salt, usually form crystalline solids with high melting points.
The second bond type is the covalent bond, which involves the sharing of valence electrons between atoms. This occurs primarily between two nonmetal atoms. Shared electrons are simultaneously attracted to the nuclei of both atoms, linking them together to form a molecule.
Covalent molecules can exist as gases, liquids, or solids with relatively low melting and boiling points. A shared pair of electrons constitutes a single covalent bond, and atoms can share multiple pairs to form double or triple bonds.
Determining Bond Type
Chemists use electronegativity to distinguish between ionic and covalent bonds. Electronegativity measures an atom’s ability to attract a shared pair of electrons toward itself within a chemical bond. This property is measured on the Pauling scale, with values ranging from approximately 0.7 to 4.0.
The difference in electronegativity (\(\Delta \text{EN}\)) between the two bonding atoms determines the bond’s character. If the atoms have the same ability to attract electrons, the difference is zero, resulting in a nonpolar covalent bond. In this case, the electrons are shared equally between the two nuclei.
A small difference in electronegativity (less than 1.7) results in a polar covalent bond. Here, the electron pair is shared unequally, spending more time closer to the atom with the higher electronegativity. This unequal sharing creates partial negative and partial positive charges on the respective atoms.
A large difference in electronegativity (greater than 1.7 or 2.0) indicates that the attraction difference is so great that a complete transfer of electrons occurs, resulting in an ionic bond. A bond between a metal and a nonmetal is conventionally classified as ionic, while a bond between two nonmetals is covalent.
Analyzing the Chlorine Molecule
Applying the principles of electronegativity to the chlorine molecule (\(\text{Cl}_2\)) provides a clear classification. \(\text{Cl}_2\) is composed of two identical chlorine atoms bonded together. Chlorine is a nonmetal found in Group 17 of the periodic table.
Since both atoms are identical, they possess the exact same electronegativity value (approximately 3.16 on the Pauling scale). Calculating the difference in electronegativity results in a value of zero (3.16 – 3.16 = 0). This zero difference is the characteristic of a nonpolar covalent bond.
The two chlorine atoms share the electron pair equally, resulting in a balanced distribution of charge across the molecule. This equal sharing satisfies the need for each chlorine atom to achieve a stable electron configuration. Therefore, \(\text{Cl}_2\) is a pure, nonpolar covalent molecule.