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

The correct order is option (c) \(\mathrm{O} > \mathrm{N} > \mathrm{P}\).

Step 1: Understand Electronegativity

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. In the periodic table, electronegativity increases across a period from left to right and decreases down a group.

Step 2: Identify Element Position

Identify the position of each element in the periodic table. Oxygen (O) and Nitrogen (N) are in the second row, while Phosphorus (P) is in the third. Oxygen and Nitrogen are both in Group 15, and Phosphorus is also in Group 15.

Step 3: Compare Electronegativity Trends

Oxygen is more electronegative than Nitrogen because it is further to the right in the periodic table. Both Oxygen and Nitrogen are more electronegative than Phosphorus, which is lower in the same group.

Step 4: List Electronegativity Values

For clarity, here are the Pauling electronegativity values: Oxygen = 3.44, Nitrogen = 3.04, Phosphorus = 2.19. So the order of electronegativity from highest to lowest is O > N > P.

Step 5: Evaluate Options

Look at the options given. Identify which one matches the correct order from our findings: O > N > P matches option (c).

Key Concepts

Pauling Electronegativity Scale

To understand electronegativity better, one must first know about the Pauling Electronegativity Scale. This scale was developed by Linus Pauling, a renowned chemist, to quantify the tendency of an atom in a molecule to attract electrons.
Pauling used the differences in bond energies as a way to calculate an electronegativity value for each element.
The Pauling scale is essential because it provides a simple numerical means of comparing the electronegativities of different elements.
Elements with higher electronegativity values on the Pauling scale are more likely to attract electrons in a chemical bond. This makes it helpful for predicting the behavior of atoms in compounds.
For example, according to this scale, oxygen has a higher electronegativity than nitrogen and phosphorus. Here's a quick look at their electronegativity values as per the Pauling scale:

• Oxygen: 3.44
• Nitrogen: 3.04
• Phosphorus: 2.19

This means that oxygen is the most effective at attracting electrons, followed by nitrogen, with phosphorus being the least electronegative of the three.

Periodic Table Trends

Electronegativity is not just a standalone concept; it is closely related to trends observed in the periodic table. When looking at the periodic table, you can observe that electronegativity generally increases as you move from left to right across a period.
This is because elements become less metallic and have lower tendencies to lose electrons, making them more electronegative.
As you move down a group, the electronegativity decreases. As you descend a group, the additional electron shells mean that the electrons are further away from the nucleus.
Hence, the attraction of the outer electrons to the nucleus becomes weaker, leading to decreased electronegativity.
In the exercise, oxygen and nitrogen are in the same period (row) as phosphorus but are positioned to the right side of the periodic table. Therefore, they are more electronegative than phosphorus.
Trends like these can help you determine the order of electronegativity of elements at a glance.

Chemical Bonding

Electronegativity is a critical factor in chemical bonding. It defines how electrons are distributed between atoms in a molecule.
When two atoms form a bond, the difference in their electronegativities determines the bond type.
Here are the most common types of bonds you might encounter based on electronegativity differences:

• Nonpolar covalent bond: When two atoms have identical or very similar electronegativities, they share electrons equally. An example is the bond between two hydrogen atoms.
• Polar covalent bond: When there is a significant difference in electronegativity between two bonded atoms, the electrons are shared unequally, leading to a polar covalent bond. A common example is the bond between hydrogen and oxygen in water (H₂O), where oxygen is more electronegative.
• Ionic bond: If the electronegativity difference is large, one atom takes an electron from the other, resulting in an ionic bond, such as the bond between sodium and chlorine in NaCl.

Understanding these bonds helps in predicting the properties and reactivity of chemical compounds, as well as the stability and solubility of the molecules they form.