Problem 75 - A Complete Resource Book in Chemistry for JEE Main

Question

In Vth group, which element has highest boiling point value? (a) \(\mathrm{Bi}\) (b) Sb (c) \(\mathrm{As}\) (d) \(\mathrm{P}\)

Step-by-Step Solution

Answer

The element with the highest boiling point in Group V is bismuth ( ).

Step 1: Identify Group V Elements

Group V elements include nitrogen ( ), phosphorus ( ), arsenic ( ), antimony ( ), and bismuth ( ). The options provided cover the elements from phosphorus to bismuth.

Step 2: Determine General Trends in Boiling Points

Boiling points of elements are influenced by the type of bonding and structure of the element. Generally, boiling points increase down a group as the atomic number increases and more electrons surround the nucleus. This enhances Van der Waals forces, hence the boiling points.

Step 3: Verify Boiling Points of Given Elements

From phosphorus to bismuth, their boiling points rise following the general trend: Phosphorus (): ~280 , Arsenic ( ): ~613 , Antimony ( ): ~1587 , Bismuth ( ): ~1837 . Here, bismuth has the highest boiling point.

Key Concepts

Boiling Point Trends in Group 15 Elements

In the world of chemistry, boiling point trends are essential to understand how different elements behave under heat. In Group 15 of the periodic table, which includes elements such as nitrogen, phosphorus, arsenic, antimony, and bismuth, boiling points increase as you move down the group. This trend is primarily due to two factors that influence boiling points:

• Increase in size and mass of the atoms.
• Increase in the strength of interatomic forces.

As the atomic number increases, elements have more electrons which contribute to stronger Van der Waals forces, thus raising their boiling points. It is insightful to see how larger elements have higher boiling points in Group 15.

Atomic Number and Boiling Point

The atomic number of an element is fundamentally related to its position on the periodic table. For the Group 15 elements, as the atomic number increases from phosphorus to bismuth, so does the boiling point. This trend can be attributed to these factors:

• More electrons in the outer shells as you go down the group.
• Increased electron shielding and distance from the nucleus.

For example, phosphorus has a boiling point of around 280°C, while bismuth's boiling point soars to approximately 1837°C. This difference is remarkable and illustrates the strong correlation between higher atomic numbers and boiling points.

Understanding Van der Waals Forces

Van der Waals forces are weak intermolecular forces that arise due to the interaction between uncharged atoms. These forces become crucial when considering why boiling points increase within Group 15 elements as you descend the group. Here’s how Van der Waals forces contribute:

• Larger atoms have more electrons, increasing the force's effect.
• These interactions get stronger as atoms become heavier and larger.

In essence, because the number of electrons increases with atomic number, the surfaces over which Van der Waals forces can act are larger, meaning that more energy (in the form of heat) is required to overcome these forces.

Chemical Bonding and Boiling Point

Chemical bonding is the heart of understanding an element's boiling point. While Van der Waals forces are significant for the Group 15 elements, other aspects of bonding impact their boiling points, notably:

• The type of bonds (covalent, ionic, metallic).
• The molecular structure and its effect on intermolecular attraction.

In Group 15, the chemical bonding generally involves covalent bonds but cultural differences in bonding and structure as elements go from nonmetals to metalloids to metals have large implications on boiling points. Bismuth, being a heavy metal, not only has metallic bonds but also a larger atomic size contributing further to its high boiling point.