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

Question

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

Step-by-Step Solution

Answer

Element (a) Bi has the highest boiling point in Group 15.

Step 1: Identify the Group

The 'Vth group' refers to Group 15 of the periodic table, also known as the nitrogen group. The elements listed: Bismuth (Bi), Antimony (Sb), Arsenic (As), and Phosphorus (P) are all part of this group.

Step 2: Understand Periodic Trends

Boiling points in Group 15 generally increase down the group. This is due to stronger van der Waals forces as a result of increased atomic size, which means more energy (higher temperature) is required to boil the element.

Step 3: Determine Order of Elements in Group 15

In Group 15, the elements are ordered from top to bottom as: Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb), and Bismuth (Bi). The boiling point tends to increase as one moves down the group.

Step 4: Compare Boiling Points

Based on the periodic trend in Group 15, Bismuth (Bi), being the heaviest and largest among these elements, will have the highest boiling point compared to the others - Phosphorus (P), Arsenic (As), and Antimony (Sb).

Key Concepts

Group 15 Elements

Group 15 of the periodic table is known for its varied and interesting elements. It is often referred to as the nitrogen group due to the inclusion of nitrogen at the top.
These elements share some common properties, which make them fascinating to study in chemistry. Group 15 includes the following elements:

• Nitrogen (N)
• Phosphorus (P)
• Arsenic (As)
• Antimony (Sb)
• Bismuth (Bi)

Each of these elements plays a vital role in various chemical reactions and in nature itself.
As you move down the group, the atomic number increases, which leads to larger atomic radii and different chemical behaviors. For example, nitrogen is a gas, while the others are solids at room temperature. This change is due to the varying strengths of intermolecular forces between atoms as the size of the atoms increases.

Boiling Points

Understanding boiling points in chemistry involves examining how elements react to heat. Boiling points are the temperatures at which a substance changes from a liquid to a gas. In Group 15, there is a clear trend: boiling points increase as you go down from nitrogen to bismuth. This trend is mainly due to van der Waals forces. These are weak forces of attraction between molecules; however, as atomic size increases, these forces become stronger, requiring more heat to break them.
For these elements:

• Nitrogen, a gas, has the lowest boiling point, due to very weak forces between molecules.
• Phosphorus exists as P₄ molecules with a higher boiling point than nitrogen because of stronger van der Waals forces.
• As we go further, arsenic, antimony, and bismuth have even heavier atoms, leading to even higher boiling points.

This concept shows how atomic size and intermolecular forces interplay to determine the boiling points of the elements.

Periodic Table Groups

The periodic table is organized into groups and periods, helping chemists understand elements better. A 'group' in the periodic table is a column of elements that have similar chemical properties. This similarity stems from having the same number of electrons in their outermost shell. Group 15 is one of these columns, and it exhibits trends in properties such as boiling points, atomic size, and ionization energy.
Why does group behavior matter?

• Predict Element Behavior: Elements in the same group react in similar ways, aiding in predicting chemical reactions.
• Understand Trends: It allows scientists to comprehend how certain properties like electronegativity, ionization energy, and atomic radii change across different elements.
• Categorize Elements: Organizing elements in groups assists in categorizing them for various applications in medicine, industry, and more.

The periodic table is a powerful tool in chemistry, organizing elements in such a systematic way that helps in easily predicting and understanding chemical behaviors and trends.