Problem 115 - 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\. Generally do not form covalent compounds Select the correct properties. (a) 1 (b) 1,3 (c) 2,3 (d) \(1,2,3\)

Step-by-Step Solution

Answer

The correct properties are option (a) 1.

Step 1: Understanding Noble Gases

Noble gases are a group of chemical elements with similar properties in the periodic table, specifically helium, neon, argon, krypton, xenon, and radon. They are characterized by their lack of reactivity due to their full valence electron shell, which makes them largely inert.

Step 2: Evaluate Property 1

Property 1 states that noble gases readily form compounds which are colourless. Noble gases are not known for readily forming compounds, but when they do, such compounds are often colorless gases or solids. Therefore, this property can be somewhat correct under certain reactive conditions or special chemicals, like XeF_2 (xenon difluoride).

Step 3: Evaluate Property 2

Property 2 mentions that noble gases generally do not form ionic compounds. This is true because noble gases are not inclined to gain or lose electrons easily due to their stable electron configurations, which makes the formation of ionic bonds unlikely.

Step 4: Evaluate Property 3

Property 3 denotes that noble gases have variable oxidation states in their compounds. This property is inaccurate. While noble gases are largely unreactive, when they do form compounds (mostly xenon), they might show some variable oxidation states, but it’s not a general characteristic.

Step 5: Evaluate Property 4

Property 4 claims that noble gases generally do not form covalent compounds. This is partially incorrect. While noble gases are mostly inert and do not commonly form covalent compounds, there are exceptions, such as xenon hexafluoroplatinate and xenon difluoride, where covalent bonding happens.

Step 6: Select the Correct Properties

Based on the evaluation, properties 1 and 2 can reasonably apply to noble gases. Property 1 is correct under certain circumstances where particular compounds are colorless. Property 2 is correct because noble gases do not typically form ionic compounds. Therefore, the correct answer is option (a) 1.

Key Concepts

Reactivity of Noble Gases

Noble gases are often considered the least reactive elements in the periodic table. The reason behind their low reactivity is their complete valence electron shell, which makes them stable and not in need of additional electrons. This stability means they have little inclination to participate in chemical reactions. However, this doesn't mean they never react. Under extreme conditions, such as at high pressures or with a strong electric field, they can form compounds, particularly with highly electronegative elements like fluorine. Some noble gases like xenon and krypton can form a limited number of compounds under these conditions.

Properties of Noble Gases

The properties of noble gases set them apart from other elements. They are characterized by:

• Having full outer electron shells, which makes them stable and largely inert.
• Being colorless, odorless, and tasteless gases at room temperature.
• Existing in monoatomic form due to their lack of reactivity.
• Having low boiling and melting points compared to other groups, making them gaseous under normal conditions.

These unique properties are why they do not readily react or form compounds. Nevertheless, when they form compounds, such as with xenon, the resulting compounds can show properties like being colorless, reinforcing the inert nature of noble gases.

Chemical Compounds of Noble Gases

For a long time, noble gases were thought not to form any compounds. However, in the 1960s, chemists discovered that some noble gases can indeed form compounds under certain conditions. Xenon, in particular, is known for forming a variety of compounds. Compounds like xenon hexafluoroplatinate (XePtF₆) and xenon difluoride (XeF₂) are examples of chemical compounds involving noble gases. When noble gases do form compounds, they frequently involve highly electronegative elements. Xenon's ability to mix with oxygen and fluorine is primarily due to its relatively large atomic size and lower ionization energy compared to smaller noble gases. These compounds often have interesting properties and can be colorless, following one of the possible traits of noble gases as being colorless. This ability to form compounds challenges the old notion of complete inertness, showing that even the most stable elements have the potential to engage in chemical reactions under suitable conditions.