Sodium (Na) and chlorine (Cl) create the compound table salt (sodium chloride). The nature of the bond holding these elements together is a direct consequence of electronegativity. Understanding their interaction requires knowing the difference in their ability to attract electrons, which dictates the compound’s chemical and physical properties.
Understanding Electronegativity
Electronegativity is a chemical property describing an atom’s “pulling power” for shared electrons within a chemical bond. It measures the tendency of an atom to attract a bonding pair of electrons toward itself when combined with another atom. This property is a relative measure of an atom’s electron-attracting ability in a compound.
The most widely accepted method for quantifying this tendency is the Pauling scale, developed by chemist Linus Pauling. This scale assigns numerical values to elements based on bond-energy calculations, generally ranging from 0.7 to 4.0 (for fluorine).
The periodic table illustrates electronegativity trends. Elements on the far left, like sodium, have low values because they readily lose outer electrons. Nonmetals toward the right, such as chlorine, have high values because they desire to gain electrons to complete their outer shell. The greater the difference between two atoms, the more unequal the sharing of bonding electrons will be.
Calculating the Difference for Sodium and Chlorine
To determine the nature of the bond, scientists use accepted electronegativity values. Sodium, a metal in Group 1, has a value of 0.93, reflecting its tendency to give up its single valence electron.
Chlorine, a halogen in Group 17, is a highly reactive nonmetal with a value of 3.16. This high number indicates its strong attraction for an additional electron to complete its outer shell. The difference is calculated by subtracting the smaller value from the larger one.
The calculation reveals the difference: \(3.16 – 0.93 = 2.23\). This figure quantifies the disparity in electron-pulling strength between the two atoms. It is the definitive data point used to predict the resulting chemical bond type and the properties of the final compound.
The Result of a Large Electronegativity Difference
The calculated electronegativity difference of 2.23 defines the nature of the bond in sodium chloride. A difference greater than approximately 1.7 or 1.8 on the Pauling scale indicates the bond has more than 50% ionic character, a threshold the value of 2.23 significantly exceeds.
This large difference means the electron is effectively transferred completely from the sodium atom to the chlorine atom. The chlorine atom strips the lone valence electron from the sodium atom. This transfer allows both atoms to achieve a stable, full outer electron shell.
This transfer results in the formation of ions. Sodium loses an electron and becomes a positively charged ion (\(Na^+\)), while chlorine gains an electron and becomes a negatively charged chloride ion (\(Cl^-\)). These oppositely charged ions are powerfully attracted to one another through electrostatic forces.
The attraction between the \(Na^+\) and \(Cl^-\) ions forms an ionic bond, creating a rigid crystal lattice structure in the solid compound. This ionic structure explains the physical properties of table salt, such as its high melting point and its ability to conduct electricity when dissolved or melted. The large electronegativity difference is the reason sodium chloride is a brittle, crystalline solid.