Which is the most electronegative element in the periodic table?

Electronegativity is the tendency of an atom in a chemical bond to attract the shared pair of electrons towards itself. It is not a property of an isolated atom but of an atom in a molecule. The concept was introduced by the American chemist Linus Pauling in 1932, who developed the most commonly used electronegativity scale, the Pauling scale.

On the Pauling scale, fluorine has the highest electronegativity of all elements, a value of about 4.0 (3.98). It is followed by oxygen (3.44), chlorine (3.16) and nitrogen (3.04). Caesium and francium have the lowest values, about 0.7-0.79.

Fluorine is the most electronegative element because:

• It has a very small atomic size, so its nucleus is very close to its outer electrons.
• It has a high effective nuclear charge.
• It needs only one electron to complete its octet.

Trends of electronegativity in the periodic table:

• Across a period (left to right), electronegativity increases, because the atoms become smaller and the nuclear charge increases.
• Down a group, electronegativity decreases, because the atoms become larger, and the outer electrons are farther from the nucleus.
• Noble gases are usually not assigned electronegativity values on the Pauling scale, because they rarely form bonds.

The difference in electronegativity between two bonded atoms decides the type of bond:

• A large difference (usually more than about 1.7) produces an ionic bond, as in sodium fluoride or sodium chloride.
• A small difference produces a polar covalent bond, as in water or hydrogen chloride.
• No difference produces a non-polar covalent bond, as in H2 or Cl2.

Fluorine is also the most reactive non-metal. It reacts with almost all elements, even with some noble gases such as xenon, forming compounds like xenon difluoride. Chlorine, however, has the highest electron affinity, slightly higher than fluorine.

Linus Pauling received the Nobel Prize in Chemistry (1954) and the Nobel Peace Prize (1962).

Why not the other options?

• ✗Oxygen is the second most electronegative element.
• ✗Chlorine has the highest electron affinity, but lower electronegativity than fluorine.
• ✗Nitrogen has an electronegativity of about 3.0.