Difficulty: Easy
Correct Answer: Oxygen (O)
Explanation:
Introduction / Context:
Electronegativity is a measure of the tendency of an atom to attract shared electrons toward itself in a chemical bond. It plays a key role in determining bond polarity, molecular structure and chemical reactivity. This question asks you to identify the most electronegative element among a small set of choices, which is a common type of periodic trends problem in exams.
Given Data / Assumptions:
Concept / Approach:
Across a period in the periodic table, electronegativity generally increases from left to right, while down a group it decreases. Nonmetals in the upper right corner (excluding the noble gases) are the most electronegative. Fluorine is the most electronegative element, but since it is not an option, we must compare oxygen, chlorine, nitrogen, sodium and aluminium. Among these, oxygen has a higher electronegativity than nitrogen and chlorine. Sodium and aluminium are metals with much lower electronegativity values. Thus, oxygen is the most electronegative element among the choices.
Step-by-Step Solution:
Step 1: Recall approximate electronegativity values on the Pauling scale: O ~ 3.5, Cl ~ 3.0, N ~ 3.0, Na ~ 0.9, Al ~ 1.5.
Step 2: Identify that sodium and aluminium are metals and generally have low electronegativities, so they can be excluded as candidates for the highest value.
Step 3: Compare the nonmetals: oxygen, chlorine and nitrogen. Among these, oxygen has an electronegativity of about 3.5, which is higher than the values for chlorine and nitrogen.
Step 4: Therefore, oxygen is the most electronegative element in the given list.
Step 5: Confirm this by periodic trends: oxygen is above sulfur and to the right of nitrogen, positioned closer to fluorine, the most electronegative element.
Verification / Alternative check:
You can verify this result by examining common chemical behaviours. Oxygen tends to form strongly polar covalent bonds with many elements, such as in water, metal oxides and oxoacids. The large electronegativity difference between oxygen and metals leads to ionic character and basic or amphoteric oxides. Chlorine is also highly electronegative, but when comparing bond polarities such as H–O versus H–Cl, the H–O bond is less polar than H–F but similar or slightly different compared with H–Cl. Nonetheless, numerical tables of electronegativity consistently place oxygen above both nitrogen and chlorine. Sodium and aluminium, being metals, readily lose electrons to form cations, which is characteristic of low electronegativity.
Why Other Options Are Wrong:
Chlorine is indeed highly electronegative, but its value is slightly lower than that of oxygen. Nitrogen has a high electronegativity but still slightly less than oxygen. Sodium has a very low electronegativity; it tends to lose its valence electron to form Na+ rather than attract electrons. Aluminium has a moderate but still relatively low electronegativity, behaving as a typical metal that can form positive ions and covalent compounds with more electronegative elements. Thus, none of these options surpass oxygen in electronegativity among the choices given.
Common Pitfalls:
A common mistake is to think that chlorine, being a halogen and located further to the right on the periodic table, must always be more electronegative than oxygen. However, electronegativity also depends on the period. Oxygen is in period 2, closer to the nucleus and with less shielding than chlorine in period 3, which increases its effective nuclear attraction for bonding electrons. Another pitfall is confusing ionisation energy with electronegativity; while they are related, they are not identical. To avoid these errors, memorise that fluorine is the most electronegative, followed by oxygen as one of the next highest among common elements.
Final Answer:
Among the listed elements, the most electronegative is oxygen (O).
Discussion & Comments