Which element is the most electronegative?

Step 1: Analyze the question Electronegativity is the ability of an atom to attract the shared pair of electrons in a covalent bond towards itself.

Step 2: Concept Electronegativity trends in the Periodic Table:

• It increases from left to right across a period (nuclear charge increases, atomic radius decreases).
• It decreases down a group (atomic radius increases and shielding increases).

So the most electronegative elements sit at the top right of the table (ignoring noble gases).

Step 3: Apply to the options

• Calcium (Group 2, Period 4): a metal, low electronegativity (about 1.0)
• Sodium (Group 1, Period 3): a metal, very low electronegativity (about 0.9)
• Iodine (Group 17, Period 5): a halogen, but low in the group because of its large size (about 2.7)
• Oxygen (Group 16, Period 2): very high (about 3.5)
• Fluorine (Group 17, Period 2): the smallest halogen, with the highest electronegativity of all elements (about 4.0 on the Pauling scale)

Step 4: Answer Fluorine is the most electronegative element. It is the top of Group 17 and is further right than oxygen in Period 2, so it has the strongest pull on bonding electrons.

Tip: Remember the order of the top electronegative elements: F > O > N ≈ Cl. A handy phrase is "Fine Old Nigerian Car" for F, O, N, Cl. For any "most electronegative" question, go to the top right of the Periodic Table, and fluorine is the winner.