Lithium (Li) is the lightest of all metals and the first element in the alkali metal group on the periodic table. Understanding its chemical behavior requires examining one fundamental property: electronegativity. This value provides insight into how lithium interacts with other elements to form compounds.
Defining Electronegativity
Electronegativity is a measure of an atom’s ability to attract a shared pair of electrons toward itself when forming a chemical bond. This concept is distinct from electron affinity, as it describes the “electron pulling power” of an atom only when it is part of a molecule, not in isolation. Since it is a relative measure based on bond energies, it is not a property that can be measured directly in a laboratory setting.
The most widely accepted system for assigning these values is the Pauling scale. This scale allows scientists to compare the electron-attracting tendencies of different elements numerically. Fluorine, the element with the strongest pull, is assigned the highest value, while elements on the opposite side of the periodic table have the lowest values.
The Specific Value for Lithium
On the Pauling scale, the electronegativity value assigned to lithium is 0.98. This is a low number compared to the full range of the scale. For context, the highest value belongs to Fluorine at 3.98, and the least electron-attracting elements, like Cesium, are around 0.79.
Lithium’s low value places it in the category of electropositive elements. This means lithium has a minimal tendency to attract electrons in a bond. Instead, lithium is more likely to give them up to another atom, which is characteristic of metals.
How Lithium’s Electronegativity Influences Bonding
The low electronegativity of 0.98 influences how lithium forms chemical structures. Lithium possesses a single valence electron, and because it has little attraction for other electrons, it readily loses this outermost electron. By shedding one electron, the lithium atom achieves the stable, filled electron shell configuration of Helium, forming a stable Li+ cation.
This tendency to donate electrons dictates that lithium primarily forms ionic bonds when reacting with non-metals. When lithium bonds with a highly electronegative element like Fluorine (3.98), the difference in their values is 3.0. This difference is greater than the threshold typically associated with ionic bonding. In the resulting compound, such as lithium fluoride (LiF), the electrons are effectively transferred to the Fluorine atom rather than being shared. This electron transfer explains lithium’s high chemical reactivity and its classification as an alkali metal.