Problem 60 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is mismatched with reference to third period? (a) largest size sodium (b) strongest oxidant chlorine (c) ionization potential of greater than nitrogen phosphorus (d) ionization potential of greater than sulphur phosphorus

Step-by-Step Solution

Answer

(c) Ionization potential of greater than nitrogen phosphorus is mismatched.

Step 1: Understanding the Periodic Trends

In the periodic table, moving across a period from left to right, atomic size generally decreases, ionization potential generally increases, and electronegativity increases.

Step 2: Verification of Each Option

(a) Sodium is at the beginning of the third period, so it has the largest size due to less nuclear charge compared to other elements in the period. This is correct. (b) Chlorine is a strong oxidizing agent due to its high electronegativity and desire to gain electrons. This is correct. (c) Phosphorus has a lower ionization potential than nitrogen, making the statement incorrect in the context of the third period. The correct order is N > P due to the stability and half-filled orbitals of nitrogen. (d) Phosphorus has a higher ionization potential than sulfur, which is true because of the number of protons and electron repulsions in sulfur's orbitals.

Step 3: Identifying the Mismatch

The mismatch in the options is option (c), as it incorrectly states that phosphorus has a higher ionization potential than nitrogen within the third period trend.

Key Concepts

Atomic Size

Atomic size refers to the distance from the center of an atom's nucleus to the outermost shell of electrons. The periodic trend for atomic size is quite informative.
As you move across a period in the periodic table, from left to right, atomic size generally decreases. Why does this happen? As you go from one element to the next, each additional electron is added to the same principal energy level, while protons are added to the nucleus.
More protons mean a higher positive charge, which attracts the electrons more strongly towards the nucleus. This increased nuclear charge causes the electrons to be pulled in closer, decreasing the atomic size.

• Sodium, being the first element in the third period, has the largest atomic size in this period.
• The increased nuclear charge as you move across a period makes the atoms smaller than those to the left.

Ionization Potential

Ionization potential, or ionization energy, is the energy required to remove an electron from an atom in its gaseous state. A key periodic trend for ionization potential must be understood to grasp its importance.
As you move from left to right across a period on the periodic table, ionization potential generally increases. This is due to the increasing nuclear charge, which holds the outer electrons more tightly, making them harder to remove.
However, there are exceptions due to electron configurations. Take, for example, phosphorus and nitrogen:

• Nitrogen has a higher ionization potential than phosphorus within the third period, due to its half-filled p orbital stability.
• Phosphorus has a slightly lower ionization potential than sulfur. Though sulfur's additional electron causes repulsion, its nuclear charge plays a role.

Understanding these exceptions is key to mastering the intricacies of ionization potential.

Oxidizing Agents

Oxidizing agents are substances that can oxidize other materials while being reduced themselves. In simpler terms, they help other substances lose electrons while they gain electrons.
For elements in the periodic table, their ability to act as oxidizing agents depends on their electronegativity. The trend in the third period is clear:

• Chlorine, at the end of the third period, is a very strong oxidizing agent.
• Its high electronegativity means it has a strong desire to gain electrons.

Chlorine's high electronegativity allows it to effectively pull electrons from substances, making it a stronger oxidizing agent than other third-period elements like sodium or phosphorus.

Third Period Elements

The third period in the periodic table includes important elements such as sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, and argon. Understanding their trends helps illustrate broader periodic principles.
A notable trend in the third period is the shift in properties from metallic to non-metallic:

• Sodium, at the start of the period, is metallic with a large atomic size and low ionization energy.
• As you move across the period, elements become less metallic, with non-metal chlorine at the other end as a strong oxidizing agent.

The third period beautifully illustrates how changes in electron configurations and nuclear charges affect atomic size, ionization potential, and oxidative ability.
Observing these elements helps deepen your understanding of how periodic trends manifest in reality.