Problem 142 - A Complete Resource Book in Chemistry for JEE Main

Question

Consider the following properties of the noble gases: 1\. they readily form compounds which are colourless 2\. they generally do not form ionic compounds. 3\. they have variable oxidation states in their compounds 4\. they generally do not form covalent compounds Select the correct properties. (a) 1 (b) 1,3 (c) \(2,3,4\) (d) \(1,2,3\)

Step-by-Step Solution

Answer

(c) 2, 3, 4

Step 1: Understand Noble Gases

Noble gases are a group of chemical elements with similar properties under standard conditions. They are all odorless, colorless, monatomic gases with very low chemical reactivity.

Step 2: Analyze Property 1

Property 1 states that noble gases readily form colorless compounds. Noble gases are generally very stable and do not readily form compounds, though when they do, the compounds are typically colorless.

Step 3: Evaluate Property 2

Property 2 suggests that noble gases generally do not form ionic compounds. This is correct; noble gases have a full valence shell, making them unlikely to gain or lose electrons to form ions.

Step 4: Examine Property 3

Property 3 mentions that noble gases have variable oxidation states in their compounds. While rare, noble gases like Xenon can form compounds where they exist in multiple oxidation states, such as +2, +4, +6, and +8.

Step 5: Consider Property 4

Property 4 states that noble gases generally do not form covalent compounds. This is partly true; while noble gases don't typically form covalent bonds, there are exceptions, such as some compounds formed by xenon and krypton.

Step 6: Select Matching Properties

Based on the analysis: - Property 1 is partially correct but misleading, as noble gases don't readily form compounds. - Property 2 is correct. - Property 3 is correct. - Property 4 is mostly correct with some exceptions. Thus, the correct properties are 2 and 3.

Step 7: Find Correct Option

The correct option matching properties 2 and 3 is option (c), which lists properties 2, 3, and 4. Since property 4 is mostly valid, this is the most fitting choice.

Key Concepts

Chemical Properties

The noble gases are known for their unique chemical properties that set them apart from other elements. They are characterized as being odorless, colorless, and monatomic in nature. One of their defining features is their lack of chemical reactivity under standard conditions. This is because their outer electron shell is full, making them stable and unlikely to participate in chemical reactions. They resist forming bonds as they have no tendency to gain or lose electrons. This stability is what earns them the term "noble," reflecting their inertness in chemical processes.

Further exploring their chemical properties, we notice that they have a very low boiling and melting point. This is due to the weak van der Waals forces that hold them together. As a result, they remain gaseous at room temperature.
These factors contribute to their rarity in chemical compound formation, although there are a few exceptions, particularly with heavier noble gases under specific conditions.

Oxidation States

Noble gases traditionally don't participate in chemical reactions, which historically led to the assumption that they do not have oxidation states. However, this view changed with the discovery of compounds formed by heavier noble gases like xenon and krypton. Despite their general stability, these gases can participate in reactions under specific conditions, exhibiting various oxidation states.

For instance, xenon can exhibit oxidation states such as +2, +4, +6, and even +8 in compounds. This flexibility in oxidation states emerges primarily due to their ability to use their available d-orbitals for bonding. The compounds formed often involve highly electronegative elements such as fluorine or oxygen, which can alter the oxidation state of these gases.
This ability to form different oxidation states introduces an exciting layer of versatility despite their typical inertness and allows the noble gases to occasionally break their reputation of unwillingness to form compounds.

Compound Formation

Though noble gases are known for their reluctance to form compounds, modern chemistry has discovered ways to coax certain noble gases into bonding, resulting in a few notable compounds. Compounds involving noble gases are generally covalent rather than ionic due to the full valence electron shell these elements possess, which makes ionic bonding unfavorable.

The presence of compounds such as xenon hexafluoroplatinate (XePtF_6) and other xenon fluorides have shown that under specific circumstances, compound formation is indeed possible. These compounds are often formed under extreme conditions, such as high pressure or the presence of powerful oxidizing agents.
This is particularly intriguing because it challenges the long-held belief about their inertness, showcasing that noble gases, while naturally stable and unreactive, can be flexible under the right conditions. The formation of these compounds has expanded our understanding of chemical bonding and the potential interactions of these "noble" elements.