SIGMA BOND Meaning and
Definition
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A sigma bond is a type of chemical bond formed between two atoms where the electron density is concentrated in the region along the line connecting the nuclei of the atoms. It is the strongest type of covalent bond and is typically formed by the direct overlap of atomic orbitals.
In a sigma bond, the electrons are shared between the two atoms, with the electron density being highest along the bond axis. This type of bond allows the atoms to share their electron pairs, resulting in a stable molecular structure. Sigma bonds can be formed between two atoms of the same element, such as in a diatomic molecule, or between different atoms in a molecule.
Sigma bonds have a cylindrical or tubular shape around the bond axis, hence the name "sigma" which refers to the Greek letter σ. They are denoted symbolically by a line between the atoms. This type of bond allows for the rotation of atoms around the bond axis, as the electron density is symmetrical along the bond.
Sigma bonds can be classified further as single, double, or triple bonds, depending on the number of electron pairs shared between the atoms. Single sigma bonds involve the sharing of one electron pair, whereas double and triple sigma bonds involve the sharing of two and three electron pairs, respectively. In summary, a sigma bond is a strong covalent bond formed by the direct overlap of atomic orbitals, with the electron density concentrated along the bond axis.
Etymology of SIGMA BOND
The word "sigma" comes from the Greek letter σ (sigma) which is the eighteenth letter of the Greek alphabet. In the context of chemistry, the term "sigma bond" refers to the type of covalent bond where the electron density is concentrated along the imaginary line drawn between the nuclei of the bonded atoms. This line is symbolized by the Greek letter σ.
The term was introduced by Sir Robert Robinson, a British chemist, in 1919 to describe this type of covalent bond. The Greek letter σ was chosen as a symbol due to its resemblance to the appearance of a covalent bond along the internuclear axis. This terminology has been widely adopted in the field of chemistry to describe this specific type of bond.
