Electronegativity is the tendency of an atom/molecule to attract electrons.

Electronegativity is a property that describes the tendency of an atom to attract electrons (or electron density) toward itself. An atom’s electronegativity is affected by both its atomic number and the size of the atom. The higher its electronegativity, the more an element attracts electrons.

On the most basic level, electronegativity is determined by factors such as the nuclear charge and the number/location of other electrons present in the atomic shells. The nuclear charge is important because the more protons an atom has, the more “pull” it will have on negative electrons. The most commonly used method of calculation for electronegativity was proposed by Linus Pauling, commonly referred to as the Pauling scale, with a range from 0.7 to 4.

As a general trend electronegativity increases across the periodic table from left to right due to the increasing number of protons in the nucleus and the same number of shells. It decreases down a group due to the increasing protons nuclear charge being canceled out by the increasing number of electron shells that shield the effect of the nuclear charge on the outer electron. Fluorine is the most electronegative element due to its relatively high number of protons and a low number of valence shells with a value ion the Pauling scale of 4.0. Compared to lithium on the other side of the periodic table, which has fewer protons but similar shells and has a value of 1.0. There are exceptions to these trends – for example, the noble gases have full valence electron shells and do not attract electrons.

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Key Points

• An atom‘s electronegativity is affected by both the element‘s atomic number and its size.

• The higher its electronegativity, the more an element attracts electrons.

• The atom with higher electronegativity, typically a nonmetallic element, is assigned a negative oxidation number, while metallic elements are typically assigned positive oxidation numbers.

Key Terms

Inner-shell electrons: Those electrons that are not in the outer shell and are not involved in the reactivity of the element.

Electronegativity: The tendency of an atom or molecule to attract electrons to itself.

Electron shell: The collective states of all electrons in an atom having the same principal quantum number (visualized as an orbit in which the electrons move).

Electron density: A representation of the probability of finding an electron in a specific location around an atom or molecule.