Problem 19 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following represents the correct order of electronegativity? (a) \(\mathrm{P}>\mathrm{O}>\mathrm{N}\) (b) \(\mathrm{N}>\mathrm{P}>\mathrm{O}\) (c) \(\mathrm{O}>\mathrm{N}>\mathrm{P}\) (d) \(\mathrm{N}>\mathrm{O}>\mathrm{P}\)

Step-by-Step Solution

Answer

(c) \(\mathrm{O} > \mathrm{N} > \mathrm{P}\) is the correct order of electronegativity.

Step 1: Understanding Electronegativity

Electronegativity is a measure of an atom's ability to attract and bind with electrons. Generally, electronegativity increases across a period and decreases down a group in the periodic table. Thus, elements on the right side of the periodic table typically have higher electronegativity.

Step 2: Positioning Elements on the Periodic Table

Nitrogen (N), Oxygen (O), and Phosphorus (P) are the elements in question. In the periodic table, all three elements are in Group 15 (nitrogen group) and Group 16 (oxygen group). Nitrogen and oxygen lie in period 2, while phosphorus is in period 3, below nitrogen.

Step 3: Determining the Electronegativity Order

Using the periodic table trends, oxygen, being the farthest right and in the smaller period (period 2), has the highest electronegativity, followed by nitrogen. Phosphorus, being in period 3, has the lowest electronegativity of the three. Thus, the order of electronegativity is Oxygen (O) > Nitrogen (N) > Phosphorus (P).

Step 4: Choosing the Correct Option

Reviewing the provided options, the correct order we identified corresponds to option (c): \(\mathrm{O} > \mathrm{N} > \mathrm{P}\). This matches our conclusion from the periodic trends.

Key Concepts

Periodic Table Trends

The periodic table is a tabular arrangement of chemical elements, ordered by their atomic number, electron configurations, and recurring chemical properties. Understanding periodic table trends is crucial in predicting an element's characteristics, such as electronegativity, atomic size, ionization energy, and more.
Electronegativity is a key trend where the ability of an atom to attract and hold onto electrons is measured. Generally, electronegativity increases as you move from left to right across a period. This is because elements have more protons in the nucleus, creating a greater attraction for electrons. Conversely, electronegativity decreases as you move down a group since the additional electron shells push the valence electrons further away from the nucleus, reducing the attractive force.
These trends help us place elements in an order based on their electronegativity, which is especially useful when comparing elements like nitrogen, oxygen, and phosphorus.

Group 15 Elements

Group 15 of the periodic table is known as the nitrogen group. It includes nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). Elements in this group have five electrons in their outermost shell, which contributes to their unique chemical properties.
Nitrogen and phosphorus are the most well-known elements from this group. They are essential for life, playing critical roles in biological molecules such as DNA and ATP.
Due to their position on the periodic table, electronegativity within this group decreases as we move down from nitrogen to bismuth. Nitrogen, being in period 2, has a higher electronegativity than phosphorus, which is in period 3. This trend aligns with the decrease of electronegativity moving down a group, as atoms increase in size and the outer electrons are further from the nucleus.

Group 16 Elements

Group 16 in the periodic table is often referred to as the oxygen group or chalcogens, and it includes oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po). These elements have six electrons in their outer shell, making them highly reactive, especially oxygen, which is vital for respiration and combustion processes.
Oxygen is one of the most electronegative elements, surpassed only by fluorine in the entire periodic table. Its high electronegativity is due to its small atomic size and high nuclear charge, allowing it to attract electrons strongly.
Within Group 16, as you descend from oxygen to polonium, electronegativity decreases. This is due to the increase in atomic size and the increasing distance between the valence electrons and the nucleus, which weakens the electron-attracting capability. Understanding these trends helps explain why oxygen has a higher electronegativity compared to nitrogen and phosphorus, influencing chemical reactions and bonding behavior.